Pneumatic Tire

ABSTRACT

A tread surface is formed from a center arc, a shoulder-side arc, and a shoulder arc, in such a manner that K 1= L 1 /(TDW×0.5) satisfies 0.6≦K 1 ≦0.8, where L 1  is an outline area that is a width from an equatorial plane to the end of the center arc and TDW is a tread development width, and K 2  satisfies 0.9≦K 1 ≦2.0, where K 2 =TR 1 /OD, TR 1  is a curvature radius of the center arc to a tire outside diameter OD. Furthermore, the tread surface is formed in such a manner that K 3= (β×TDW)/( 100 ×SW) satisfies 0.40≦K 3 ≦0.48, where β is an aspect ratio, and SW is a total width.

TECHNICAL FIELD

The present invention relates to a pneumatic tire, and moreparticularly, to a pneumatic tire including a tread surface with across-sectional shape formed of a plurality of arcs.

BACKGROUND ART

In a conventional tire, an area to be used on a tread when a vehicletravels straight is different from that used when the vehicle travelsaround a curve. Hence, the degree of wear may vary from point to pointacross the tread depending on a traveling condition, and accordingly,uneven tread wear may occur. Some conventional tires have a tread in ashape appropriate to reduce uneven tread wear. For example, according toPatent Document 1, to achieve a uniform contact pressure distributionand a uniform contact length distribution over the tread, the crown ofthe tread is formed from three arcs that have respective differentcurvature radiuses, and each of the arcs is formed to have anappropriate curvature radius, and an appropriate width in the tire widthdirection. Accordingly, the tread wears uniformly along the crown-widthdirection even when traveling under various conditions and the uneventread wear can be reduced.

Patent Document 1: Japanese Patent Application Laid-Open No. H9-71107

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

As described, conventional pneumatic tires are designed to reduce uneventread wear with an appropriate crown shape. Characteristics of apneumatic tire in contact with the ground vary also depending on a loadapplied to the tread. For example, a change in a load applied to thetread changes the maximum cornering force of a vehicle when turninground to which the pneumatic tire is installed. The maximum corneringforce affects the driving stability and the rollover resistance of thevehicle, which are incompatible, however, demands for improvements inthe driving stability and the rollover characteristics have beenincreased because of a strong trend toward a higher center of gravity ofa vehicle and a lower aspect ratio of a pneumatic tire.

The present invention has been made in view of the above aspect, and anobject of the present invention is to provide a pneumatic tire withwhich the driving stability can be retained and also the rollovercharacteristics can be improved.

Means for Solving Problem

To solve the above problems and to achieve the object, a pneumatic tireaccording to the present invention includes a sidewall potion arrangedon each edge of a tire width direction; and a tread portion including acap tread and is provided on the sidewall potions tire-radially-outward,the cap tread in a meridian cross section of the pneumatic tire having atread surface formed from a plurality of arcs with different curvatureradiuses. Under a condition when the pneumatic tire is mounted on aproper rim, and filled with an internal pressure of 5% of a normalinternal pressure, the tread surface is formed from a center arccentered in the tire width direction, a shoulder-side arc positioned ona vehicle-outer-side at least from the center arc in the tire widthdirection, and a shoulder arc that forms a shoulder arranged at least avehicle-outer-side end in the tire width direction of the tread surface.When TR1 is a curvature radius of the center arc, L1 is an outline area,which is a width from an equatorial plane to an end of the center arc inthe tire width direction, TDW is a tread development width, which is awidth of the tread surface in the tire width direction, SW is a totalwidth, which is a width in the tire width direction between outermostpositions in the tire width direction of the sidewall potions opposed asarranged at both edges of the tire width direction, OD is a tire outsidediameter, which is a diameter of the pneumatic tire at a position atwhich a diameter of the tread surface in a tire-radial direction islargest, and β is an aspect ratio, K1 satisfies 0.6≦K1≦0.8, K1 beingobtained from a following equation (1), which is a relation between theoutline area L1 and the tread development width TDW, K2 satisfies0.9≦K1≦2.0, K2 being obtained from a following equation (2), whichobtains a ratio of the curvature radius TR1 of the center arc to thetire outside diameter OD, and K3 satisfies 0.40≦K3≦0.48, K3 beingobtained from a following equation (3), which is a relation between theaspect ratio β, the tread development width TDW, and the total width SW,

K1=L1/(TDW×0.5)  (1)

K2=TR1/OD  (2)

K3=(P×TDW)/(100×SW)  (3).

According to the present invention, the profile of the tread surface canbe approximated to a flat shape, by calculating the relation K1 betweenthe outline area L1 and the tread development width TDW according to theabove equations, and setting K1 to satisfy 0.6≦K1≦0.8, and setting theratio K2 between the curvature radius TR1 of the center arc and theoutside diameter OD of the tire, to satisfy 0.9≦K2≦2.0. Accordingly, forexample, the contact area at low load, for example, 40% of the maximumload, can be increased, so that the maximum cornering force at low loadcan be improved. Consequently, the driving stability at low load can beassured. In addition, by calculating the relation K3 between the aspectratio β, the tread development width TDW, and the total width SW, inaccordance with the above equations, to satisfy 0.40=<K3=<0.48, thetread development width can be narrowed, so that the contact area athigh load, for example, at the maximum load, i.e., at 100% of themaximum load, can be decreased, and the maximum cornering force at highload can be reduced. Accordingly, the rollover resistance at high loadcan be improved. As a result, the rollover characteristics can beimproved while retaining the driving stability.

Furthermore, with the pneumatic tire according to the present invention,an angle α formed by a tangent in contact with the center arc and atangent in contact with the shoulder arc satisfies 35°≦α≦60°, thetangent in contact with the center-arc passing through an end in thetire width direction of the center-arc, and the tangent in contact withthe shoulder-arc passing through an outer end in the tire widthdirection of the shoulder arc.

According to the present invention, by designing the angle α to satisfy35°≦α≦60°, an angle can be changed largely around the shoulder from thetread surface direction to the sidewall direction, in other words, theshoulder can drop at a steep angle. Accordingly, an expansion of thecontact width at high load and a large slip angle can be suppressed, sothat the maximum cornering force at high load can be reduced moresecurely, and the rollover resistance at high load can be improved moresubstantially. As a result, the rollover characteristics can be improvedmore reliably.

Moreover, with the pneumatic tire according to the present invention,when SHR is a curvature radius of the shoulder arc, K4 satisfies0.025≦K4≦0.035, K4 being obtained from a following equation (4), whichobtains a ratio of the curvature radius TR1 of the center arc to thecurvature radius SHR of the shoulder arc,

K4=SHR/TR1   (4).

According to the present invention, by designing the ratio K4 of thecurvature radius TR1 of the center arc to the curvature radius SHR ofthe shoulder arc to satisfy 0.025≦K4≦0.035, the curvature radius of theshoulder can be shortened. Accordingly, an expansion of the contactwidth at high load and a large slip angle can be suppressed, so that themaximum cornering force at high load can be reduced more securely, andthe rollover resistance at high load can be improved more substantially.As a result, the rollover characteristics can be improved more reliably.

Furthermore, with the pneumatic tire according to the present invention,at least a part of the cap tread uses a compound of which a 300%-tensilemodulus is 5 MPa to 10 MPa.

According to the present invention, because the rollover characteristicsare largely affected by the compound of the cap tread that the treadincludes, improvement in the rollover resistance is designed by usingthe compound of which 300% tensile modulus is in the range from 5 MPa to10 MPa for at least a part of the cap tread. In other words, by usingsuch compound for at least a part of the cap tread, the friction forcein the tire width direction at high load and a large slip angle can bereduced, so that the rollover resistance can be improved. As a result,the rollover characteristics can be improved more reliably.

Moreover, with the pneumatic tire according to the present invention, atleast a part of the cap tread uses anisotropic rubber in which a modulusin the tire width direction is smaller than a modulus in tirecircumferential direction.

According to the present invention, improvement in the rolloverresistance is designed by using anisotropic rubber in which a modulus inthe tire width direction is smaller than a modulus in tirecircumferential direction for at least a part of the cap tread. In otherwords, by using such anisotropic rubber for at least a part of the captread, the friction force in the tire width direction at high load and alarge slip angle can be reduced, so that the rollover resistance can beimproved. As a result, the rollover characteristics can be improved morereliably.

Furthermore, with the pneumatic tire according to the present invention,a plurality of circumferential grooves that are formed in a tirecircumferential direction are further provided on the tread surface, anda shoulder-side circumferential groove from among the circumferentialgrooves that is a circumferential groove arranged most closely to theshoulder between the equatorial plane and the shoulder is provided at aposition at which T1 satisfies 0.55≦T1≦0.65, when T1 is obtained from afollowing equation (5), which is a relation between a distance H1 andthe tread development width TDW, the distance H1 being from agroove-width center of the shoulder-side circumferential groove to theequatorial plane in the tire width direction

T1=H1/(TDW×0.5)  (5).

According to the present invention, the shoulder-side circumferentialgroove is provided by calculating the relation T1 between the distanceH1 from the groove-width center of the shoulder-side circumferentialgroove to the equatorial plane and the tread development width TDW inaccordance with Equation (5) to satisfy 0.55≦T1≦0.65, so that therollover resistance can be improved while retaining the drivingstability more reliably. In other words, when the distance H1 from theequatorial plane to the groove-width center of the shoulder-sidecircumferential groove is smaller than 55% of a half of the treaddevelopment width TDW, because the shoulder-side circumferential grooveis positioned too inside in the tire width direction, there is apossibility that the rigidity of the tread in the vicinity of the centerin the tire width direction is too low. Consequently, there is apossibility that the driving stability is declined.

In another case, when the distance H1 from the equatorial plane to thegroove-width center of the shoulder-side circumferential groove islarger than 65% of a half of the tread development width TDW, becausethe shoulder-side circumferential groove is positioned too outside inthe tire width direction, there is a possibility that the rigidity ofthe tread in the vicinity of the center in the tire width direction istoo high. Consequently, there is a possibility that the maximumcornering force is increased, and the degree of improvement in therollover resistance is diminished. For this reason, by designing theshoulder-side circumferential groove to have the relation between thedistance H1 from the groove-width center of the shoulder-sidecircumferential groove to the equatorial plane and the tread developmentwidth TDW that satisfies 0.55≦T1≦0.65, the rigidity of the tread in thevicinity of the center in the tire width direction can becomeappropriate. As a result, the rollover characteristics can be improvedwhile retaining the driving stability more reliably.

Moreover, with the pneumatic tire according to the present invention, anequatorial-plane-side circumferential groove shoulder-sidecircumferential groove from among the circumferential grooves that is acircumferential groove arranged most closely to the equatorial planebetween the equatorial plane and the shoulder is provided at a positionat which T2 satisfies 0.15≦T2≦0.20, when T2 is obtained from a followingequation (6), which is a relation between a distance H2 and the treaddevelopment width TDW, the distance H2 being from a groove-width centerof the equatorial-plane-side circumferential groove to the equatorialplane in the tire width direction

T2=H2/(TDW×0.5)  (6).

According to the present invention, the equatorial-plane-sidecircumferential groove is provided by calculating the relation T2between the distance H2 from the groove-width center of theequatorial-plane-side circumferential groove to the equatorial plane andthe tread development width TDW in accordance with Equation (6) tosatisfy 0.15≦T2≦0.20, so that the driving stability can be assured moresecurely. In other words, when the distance H2 from the equatorial planeto the groove-width center of the equatorial-plane-side circumferentialgroove is smaller than 15% of a half of the tread development width TDW,because the equatorial-plane-side circumferential groove is positionedtoo inside in the tire width direction, or too close to the equatorialplane, there is a possibility that the rigidity of the tread in thevicinity of the center in the tire width direction is too low.Consequently, there is a possibility that a response of the pneumatictire to cornering is declined.

In another case, when the distance H2 from the equatorial plane to thegroove-width center of the equatorial-plane-side circumferential grooveis larger than 20% of a half of the tread development width TDW, becausethe equatorial-plane-side circumferential groove is positioned toooutside in the tire width direction, there is a possibility that therigidity of the tread in the vicinity of the center in the tire widthdirection is too high. Consequently, there is a possibility that aresponse of the pneumatic tire to cornering is too sensitive. For thisreason, by designing the equatorial-plane-side circumferential groove tohave the relation between the distance H2 from the groove-width centerof the equatorial-plane-side circumferential groove to the equatorialplane and the tread development width TDW that satisfies 0.15≦T2≦0.20,the rigidity of the tread in the vicinity of the center in the tirewidth direction can become appropriate. As a result, a response of thepneumatic tire to cornering can be appropriate, so that the drivingstability can be assured more securely.

Furthermore, with the pneumatic tire according to the present invention,the tread portion is formed from tread rubber that includes at least thecap tread, and a base rubber ply that is arranged tire-radially inwardfrom the cap tread, the base rubber ply has a JIS-A hardness between 48and 60 at room temperature, and a cross sectional area of the baserubber ply in the meridian cross section is within a range from 20% to50% of a cross sectional area of the tread rubber.

According to the present invention, a cross sectional area of the baserubber ply with a low hardness is formed to fall within the range from20% to 50% of the cross sectional area of the tread rubber. That is, athickness of the base rubber ply is made relatively thick in the treadrubber. Accordingly, the rigidity of the whole of the tread rubber,i.e., the rigidity of the whole tread, can be decreased, so that themaximum cornering force at high load can be reduced. Consequently, therollover resistance at high load can be improved. Moreover, because themaximum cornering force at high load can be reduced by decreasing therigidity of the whole tread, the cap tread can use a rubber that has ahigher grip performance. Accordingly, the maximum cornering force at lowload can be increased, so that the driving stability and the brakingperformance at low load can be improved. As a result, the rollovercharacteristics can be improved while retaining the driving stability.

Moreover, with the pneumatic tire according to the present invention, abead in which a bead core is arranged is provided tire-radially inwardon the sidewall potion, and a bead filler is provided tire-radiallyoutward from the bead core, when Hs is a JIS-A hardness of the beadfiller at room temperature, and FH is a filler height, which is adistance between an outward edge and a most distant point in the beadfiller, the outward edge being a position tire-radially most outward ofthe bead filler in the meridian cross section, G satisfies 6≦G≦11, Gbeing obtained from a following equation (7), which is a relationbetween the JIS-A hardness of the bead filler Hs, the filler height FH(mm), the tire outside diameter OD, and the aspect ratio β

G=(Hs×FH)/(OD×β)  (7).

According to the present invention, the bead filler is provided bycalculating the relation G between the Japanese Industrial Standards(JIS)-A hardness Hs of the bead filler at room temperature, the fillerheight FH, the tire outside diameter OD, and the aspect ratio β inaccordance with Equation (7) to satisfy 6≦G≦11, so that the rigidity ofthe bead filler can be appropriate. In other words, when G is smallerthan 6, because the hardness Hs of the bead filler is too low, or thefiller height FH is too low, there is a possibility that to retain thedriving stability at low load is difficult. On the other hand, when G islarger than 11, because the hardness Hs of the bead filler is too high,or the filler height FH is too high, there is a possibility that therigidity of the bead filler is too high, consequently, there is apossibility that to reduce the maximum cornering force at high load isdifficult.

For this reason, the rigidity of the bead filler can become appropriateby designing the bead filler to have the relation between the JIS-Ahardness Hs of the bead filler at room temperature, the filler heightFH, the tire outside diameter OD, and the aspect ratio β that satisfies6≦G≦11. Accordingly, the driving stability at low load can be assuredmore securely, and the maximum cornering force at high load can bereduced. As a result, the rollover characteristics can be improved whileretaining the driving stability more reliably.

Furthermore, with the pneumatic tire according to the present invention,when the outline area on the vehicle-outer-side in the tire widthdirection differs from that on the vehicle inner side in the tire widthdirection, the outline area L1 is the outline area on thevehicle-outer-side in the tire width direction, and the K1 to beobtained from the equation (1) is a relation between the outline area L1on the vehicle-outer-side in the tire width direction, and the treaddevelopment width TDW, and L1 _(in) is the outline area on the vehicleinner side in the tire width direction, a relation between K1 _(in) andK1 satisfies K1 _(in)≦K1×0.9, K1 _(in) being obtained from a followingequation (8), which is a relation between the outline area K1 _(in) andthe tread development width TDW

K1_(in) =L1_(in)/(TDW×0.5)  (8).

According to the present invention, the outline area on thevehicle-outer-side in the tire width direction differs from the that onthe vehicle inner side in the tire width direction, and the relation K1_(in) between the outline area L1 _(in) on the vehicle-inner-side in thetire width direction and the tread development width TDW is equal to 0.9times of or less than the relation K1 between the outline area L1 on thevehicle-outer-side in the tire width direction and the tread developmentwidth TDW. Accordingly, the outline area on the vehicle inner side inthe tire width direction is smaller, so that the tread surface on thevehicle inner side in the tire width direction has a larger area inwhich the shoulder-side arc and the shoulder arc are formed as comparedwith the tread surface on the vehicle-outer-side in the tire widthdirection. Thus, when the vicinity of the shoulder on the vehicle innerside in the tire width direction is in contact with the ground, a toohigh contact pressure can be suppressed, so that wear caused by the toohigh contact pressure can be prevented. On the other hand, when thevicinity of the shoulder on the vehicle-outer-side in the tire widthdirection is in contact with the ground, the rollover characteristicscan be improved. As a result, the rollover characteristics and the wearresistance can be improved.

Moreover, with the pneumatic tire according to the present invention,the K1 _(in) satisfies 0.4≦K1 _(in)≦0.6.

According to the present invention, because K1 _(in) is designed tosatisfy 0.4≦K1 _(in)≦0.6, retention of the maximum cornering force atlow load, and reduction in the contact pressure on the vicinity of theshoulder on the vehicle inner side in the tire width direction incontact with the ground can be both achieved. In other words, when K1_(in) is less than 0.4, because the outline area K1 _(in) on the vehicleinner side in the tire width direction is too small, there is apossibility that the maximum cornering force at low load is too small.On the other hand, when K1 _(in) is more than 0.6, because the outlinearea K1 _(in) on the vehicle inner side in the tire width direction isnot very narrow, there is a possibility that the contact pressure on thevicinity of the shoulder on the vehicle-inner-side in the tire widthdirection in contact with the ground cannot be reduced effectively.Therefore, retention of the maximum cornering force at low load, andreduction in the contact pressure on the vicinity of the shoulder on thevehicle inner side in the tire width direction in contact with theground can be both achieved by designing the relation K1 _(in) betweenthe outline area L1 _(in) on the vehicle inner side in the tire widthdirection and the tread development width TDW to satisfy 0.4≦K1_(in)≦0.6. As a result, the rollover characteristics and the wearresistance can be improved.

Furthermore, with the pneumatic tire according to the present invention,a belt ply is provided tire-radially inward from the tread portion, anda belt cover ply is provided tire-radially outward from the belt ply,and the belt cover ply includes a central region that contains areinforcing cord and is centered in the tire width direction, andshoulder regions that are positioned on both sides of the central regionin the tire width direction. A ratio of a cover tensile-rigidity indexEc in the center region to a cover tensile-rigidity index Es in theshoulder region satisfies 1.0<Es/Ec, when the cover tensile-rigidityindex Ec in the center region is obtained from a following equation (9),where Dc is number of reinforcing cords per 50 mm in a direction ofarrangement of the reinforcing cord arranged in the center region, andSc is an extension rate (%) of one of the reinforcing cords arranged inthe center region when a load of 50 N is applied. The covertensile-rigidity index Es in the shoulder region is obtained from afollowing equation (10), where Ds is number of reinforcing cords per 50mm in a direction of arrangement of the reinforcing cord arranged in theshoulder region, and Ss is an extension rate (%) of one of thereinforcing cords arranged in the shoulder region when a load of 50 N isapplied

Ec=Dc/Sc  (9)

Es=Ds/Ss  (10).

According to the present invention, because the belt cover ply is formedto have the ratio of the cover tensile-rigidity index Es in the shoulderregion to the cover tensile-rigidity index Ec in the central region thatsatisfies 1.0<Es/Ec, a change in the contact length in contact of thevicinity of the shoulder with the ground can be small. In other words,when Es/Ec is 1.0 or less, precisely, when the ratio of the covertensile-rigidity index Es in the shoulder region is less than the covertensile-rigidity index Ec in the central region, the rigidity of thebelt cover ply in the shoulder region is lower than the rigidity in thecenter region, so that the contact length can easily change in contactof the vicinity of the shoulder with the ground. For this reason, thereis a possibility that effective reduction in the maximum cornering forceat high load is difficult in contact of the vicinity of the shoulderwith the ground. Therefore, by forming the belt cover ply to have theratio of the cover tensile-rigidity index Es in the shoulder region tothe cover tensile-rigidity index Ec in the central region that satisfies1.0<Es/Ec, the cover tensile-rigidity index Es in the shoulder regioncan be made larger than the cover tensile-rigidity index Ec in thecentral region more substantially, so that a change in the contactlength in contact of the vicinity of the shoulder with the ground can besmall. As a result, the rollover characteristics can be improved morereliably.

Moreover, with the pneumatic tire according to the present invention, alug groove is formed on the shoulder, and a recess is formed at a groovebottom of the lug groove outward from a contact end of the tread portionin the tire width direction.

According to the present invention, because the recesses are formed atthe bottom of the lug groove arranged outward in the tire widthdirection from the contact end of the tread, the rigidity of the landportion (rigidity in a shearing direction) in a region outward from thecontact end in the tire width direction, i.e., in the non-contact regionwhen traveling normally, can be reduced. Accordingly, when the regionoutward from the contact end in the tire width direction is in contactwith the ground at high load and a large slip angle, for example, whenturning, the land portion with a lower rigidity can be brought intocontact with the ground. Thus, the maximum cornering force at high loadcan be reduced more securely. In addition, the recesses are arrangedoutward from the contact end in the tire width direction, and whentraveling normally, the region inward from the contact end in the tirewidth direction is in contact with the ground. In this manner, theregion in which the recessed are arranged is not contact with the groundwhen traveling normally, such as at low load, so that the maximumcornering force at low load can be retained without influence fromarrangement of the recesses. Accordingly, the driving stability at lowload can be assured. As a result, the rollover characteristics can beimproved while retaining the driving stability more reliably.

Furthermore, with the pneumatic tire according to the present invention,a depth H and an average D satisfy 0.20≦H/D≦0.50, where H is a depth ofthe recess at a deepest point, and D is an average of groove depths D1and D2 of the lug groove at both ends of the recess in the tire widthdirection.

According to the present invention, the ratio H/D of the depth H of therecess to the groove depth D of the lug groove is appropriatelydesigned, so that the rigidity of the land portion can be reduced moresecurely, and the thickness of rubber in areas in which the recesses areprovided can be prevented from being excessively thin. As a result, therollover characteristics can be improved more reliably, and thedurability can also be improved.

Moreover, with the pneumatic tire according to the present invention, inthe recess, an opening area decreases from an opening of the recesstoward a deepest point of the recess.

According to the present invention, an opening area of the recessgradually decreases as it extends from the opening toward the deepestpoint of the recess, so that the mold can be easily withdrawn from therecess when molding an pneumatic tire. As a result, the recess can beeasily formed.

Furthermore, with the pneumatic tire according to the present invention,the recess is arranged between a contact end and a limit contact end,when the limit contact end is set at a point distant 1.3 times of adistance from a center of contact width of the tread portion to thecontact end.

According to the present invention, the recesses are appropriatelyarranged in the tread, so that the driving stability and the durabilitycan be improved together.

Moreover, with the pneumatic tire according to the present invention, inthe recess, a cross sectional area gradually increases as toward outwardin the tire width direction.

According to the present invention, because the cross-sectional area ofthe recess gradually increases as it extends outward in the tire widthdirection, the rigidity of the land portion in the vicinity of therecess gradually decreases as it extends outward in the tire widthdirection. Therefore, the driving stability can be retained at a largeslip angle, as compared with a configuration in which the rigidity ofthe land portion drops from the vicinity of the contact end. As aresult, retention of the driving stability and improvement in therollover characteristics can be both achieved.

EFFECT OF THE INVENTION

The pneumatic tire according to the present invention brings an effectthat the rollover characteristics are improved while retaining thedriving stability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a meridian cross section that depicts a relevant part of apneumatic tire according to the present invention;

FIG. 2 is a detailed view of a portion A in FIG. 1;

FIG. 3 is an explanatory view of a circumferential groove of thepneumatic tire shown in FIG. 1;

FIG. 4 is a view of a tread as a modified example of the pneumatic tireaccording to the embodiment;

FIG. 5 is an explanatory view of the tread and a bead filler of thepneumatic tire shown in FIG. 1;

FIG. 6 is an explanatory view that depicts a modified example of thepneumatic tire according to the embodiment;

FIG. 7 is an explanatory view that depicts a modified example of thepneumatic tire according to the embodiment;

FIG. 8 is an explanatory view that depicts a modified example of thepneumatic tire according to the embodiment;

FIG. 9 is an explanatory view that depicts a modified example of thepneumatic tire according to the embodiment;

FIG. 10 is a view viewed from an arrow-headed line B-B in FIG. 9;

FIG. 11 is a detailed view of a portion C shown in FIG. 9;

FIG. 12 is an explanatory view of a recess formed in a tapering shape,and is a cross sectional view along a line D-D in FIG. 10;

FIG. 13 is an explanatory view of the recess formed in a tapering shape,and is a cross sectional view along a line E-E in FIG. 10;

FIG. 14 is an explanatory view of a recess that forms a curved surface,and is a cross sectional view along the line D-D in FIG. 10;

FIG. 15 is an explanatory view of the recess that forms a curvedsurface, and is a cross sectional view along the line E-E in FIG. 10;

FIG. 16 is an explanatory view of a modified example of the recess, andis a cross sectional view along the line B-B of FIG. 9;

FIG. 17 is an explanatory view of a modified example of the recess, andis a cross sectional view along the line E-E of FIG. 10;

FIG. 18 is an explanatory view of a modified example of the recess, andis a cross-sectional view along the line E-E of FIG. 10;

FIG. 19 is a table that indicates results of performance evaluationtests conducted by a first test method;

FIG. 20-1 is a table that indicates results of performance evaluationtests conducted by a second test method.

FIG. 20-2 is a table that indicates results of the performanceevaluation tests conducted by the second test method;

FIG. 21-1 is a table that presents compositions of rubber used forpneumatic tires on which performance evaluation tests are conducted by athird test method;

FIG. 21-2 is a table that presents the compositions of rubber used forpneumatic tires on which the performance evaluation tests are conductedby the third test method;

FIG. 22-1 is a table that indicates results of the performanceevaluation tests conducted by the third test method;

FIG. 22-2 is a table that indicates results of the performanceevaluation tests conducted by the third test method;

FIG. 23-1 is a table that indicates results of performance evaluationtests conducted by a fourth test method;

FIG. 23-2 is a table that indicates results of the performanceevaluation tests conducted by the fourth test method;

FIG. 24 is a table that indicates results of performance evaluationtests conducted by a fifth test method;

FIG. 25 is a table that presents characteristics of reinforcing cordsused for pneumatic tires on which performance evaluation tests areconducted by a sixth test method;

FIG. 26-1 is a table that indicates results of the performanceevaluation tests conducted by the sixth test method;

FIG. 26-2 is a table that indicates results of the performanceevaluation tests conducted by the sixth test method;

FIG. 27 is a table that presents detailed profiles of pneumatic tires onwhich performance evaluation tests are conducted by a seventh testmethod; and

FIG. 28 is a table that indicates results of the performance evaluationtests conducted by the seventh test method.

EXPLANATIONS OF LETTERS OR NUMERALS

-   -   1 Pneumatic tire    -   5 Equatorial plane    -   10 Tread    -   11 Tread surface    -   12 Cap tread    -   13 Rib    -   15 Sidewall    -   16 Shoulder    -   21 Belt ply    -   22 Carcass    -   23 Inner liner    -   24 Bead    -   25 Bead core    -   26 Bead filler    -   27 Outward edge    -   28 Inner-side inward edge    -   29 Outer-side inward edge    -   31 Center arc    -   32 Shoulder-side arc    -   33 Shoulder arc    -   34 Side arc    -   35 Center-arc end    -   36 Shoulder-arc end    -   41 Center-arc tangent    -   42 Shoulder-arc tangent    -   45 Shoulder-side arc extension    -   46 Side-arc extension    -   47 Virtual tread edge    -   50 Circumferential groove    -   51 Shoulder-side circumferential groove    -   52 Groove-width center    -   53 Groove-width-direction edge line    -   55 Equatorial-plane-side circumferential groove    -   56 Groove-width center    -   57 Groove-width-direction edge line    -   60 Tread rubber    -   61 Base rubber ply    -   62 Wing chip    -   70 Belt cover ply    -   71 Central region    -   72 Shoulder region    -   75 Reinforcing cord    -   76 Central-region reinforcing cord    -   77 Shoulder-region reinforcing cord    -   80 Lug groove    -   81 Groove bottom    -   83 Block portion    -   85 Recess    -   86 Sidewall    -   90 Contact end    -   91 Limit contact end

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Exemplary embodiments of a pneumatic tire according to the presentinvention are described in detail below with reference to theaccompanying drawings. The present invention is not limited by theembodiments. The constituents of the embodiments include constituentsthat can be easily replaced by those skilled in the art and constituentssubstantially same as the constituents of the embodiments.

EMBODIMENT

In the following descriptions, the tire width direction is a directionparallel to the rotation axis of a pneumatic tire; the tire widthdirection inward is a direction toward the equatorial plane in the tirewidth direction; the tire width direction outward is a direction towardthe side opposite to the equatorial plane in the tire width direction;the tire-radial direction is a direction orthogonal to the rotationaxis; and the tire circumferential direction is a direction of rotationabout the rotation axis. FIG. 1 is a meridian cross section that depictsa relevant portion of the pneumatic tire according to the presentinvention. In the meridian cross section of a pneumatic tire 1 shown inFIG. 1, the pneumatic tire 1 includes a tread portion 10 that isprovided at the tire-radially outmost portion of the pneumatic tire 1. Asidewall 15 is provided from the edge of the tread portion 10 in thetire width direction, that is, from the vicinity of a shoulder 16, to acertain point of the tire-radially inward. In other words, the sidewall15 is provided on each of both edges of the pneumatic tire 1 in the tirewidth direction. On the tire-radially inward of the sidewall 15, a bead24 is provided. Another bead 24 is also provided on the other side ofthe sidewall 15, so that two beads 24 are arranged in the pneumatic tire1 symmetrically with respect to an equatorial plane 5. A bead core 25 isprovided to the bead 24, and a bead filler 26 is provided to thetire-radially outward of the bead core 25.

A plurality of belt plies 21 are provided to the tire-radially inward ofthe tread portion 10. A carcass 22 is continuously provided to thetire-radially inward of the belt plies 21 on a side of the sidewalls 15facing to the equatorial plane 5. The carcass 22 is bent outward in thetire width direction in each of the beads 24 along the bead core 25. Aninner liner 23 is formed along the carcass 22 inward of the carcass 22,or on the inner side of the carcass 22 in the pneumatic tire 1.

The tread portion 10 includes a cap tread 12. The cap tread 12 ispositioned on the tire-radially outward of the tread portion 10, and isexposed to the outside of the pneumatic tire 1. The portion of the captread 12 exposed to the outside, that is, the surface of the cap tread12 is formed as a tread surface 11. The compound from which the captread 12 is made has a 300% tensile modulus of 5 MPa to 10 MPa. In otherwords, the property of the compound from which the cap tread 12 is madefalls within the range from 5 MPa to 10 MPa of the 300% tensile modulusdefined by JIS-K6251.

The 300% tensile modulus of the cap tread 12 in the tire width directionis smaller than that in the tire circumferential direction. In otherwords, the cap tread 12 is made from anisotropic rubber that has atensile modulus in the tire width direction smaller than that in thetire circumferential direction, and the compound that forms the captread 12 uses the anisotropic rubber.

In the meridian cross section of the pneumatic tire 1, a plurality ofarcs having different curvature radiuses form the surface of the captread 12 or the tread surface 11 serving as the surface of the treadportion 10. Specifically, a center arc 31, a shoulder-side arc 32 and ashoulder arc 33 form the tread surface 11 of the pneumatic tire mountedon a regular rim with an inner pressure of 5% of a regular innerpressure. The regular rim includes “regular rim” defined by JapanAutomobile Tire Manufacturers Association (JATMA), “design rim” definedby Tire and Rim Association (TRA), and “measuring rim” defined byEuropean Tire and Rim Technical Organization (ETRTO). The regular innerpressure includes “maximum air pressure” defined by JATMA, the maximumvalue defined by TRA as described in “tire load limits at various coldinflation pressures”, and “inflation pressure” defined by ETRTO.However, the regular inner pressure is 180 kPa to the pneumatic tire 1for passenger cars.

The center arc 31 among the arcs forming the tread surface 11 iscentered in the tire width direction on the tread surface 11, includesthe equatorial plane 5, and extends both sides of the equatorial plane 5in the tire width direction as the equatorial plane 5 is centered. Thecenter arc 31 forms an arc shape in convex outward in the tire-radialdirection, of which a radius from the vicinity of the equatorial plane 5in the tire-radial direction is the largest.

The shoulder-side arc 32 is positioned on the vehicle-outer side of thecenter arc 31 in the tire width direction or on each of both sides ofthe center arc 31. The shoulder-side arc 32 forms an arc shape in convexoutward in the tire-radial direction. The shoulder arc 33 is positionedon the outer side of the shoulder-side arc 32 in the tire widthdirection. The shoulder arc 33 forms the shoulder 16, and forms an arcshape in convex outward in the tire-radial direction.

In other words, on the tread surface 11, the shoulder-side arc 32 ispositioned on the vehicle-outer side or the both sides of the center arc31 in the tire width direction, which is in the center of the tirewidth. The shoulder arc 33 is positioned on the vehicle-outer side orthe both sides on the outer side of the shoulder-side arc 32 in the tirewidth direction. The center arc 31 and the shoulder-side arc 32 areconnected to each other and continuously formed, and the shoulder-sidearc 32 and the shoulder arc 33 are connected to each other andcontinuously formed. A curvature radius TR1 of the center arc 31, acurvature radius TR2 of the shoulder-side arc 32, and a curvature radiusSHR of the shoulder arc 33, respectively, which are positioned asdescribed above, are different from one another.

Here, the vehicle-outer side in the tire width direction is an edge sidepositioned outward in the vehicle-width direction from among the twoedges of the pneumatic tire 1 in the tire width direction when thepneumatic tire 1 is installed in a vehicle (not shown). The vehicleinner side in the tire width direction is an edge side positioned inwardin the vehicle-width direction, or an edge side toward the center in thevehicle-width direction, from among the two edges of the pneumatic tire1 in the tire width direction.

A side arc 34 is formed on the outer side of the shoulder arc 33 in thetire width direction. While being on the outer side of the shoulder arc33 in the tire width direction, the side arc 34 is connected to theshoulder arc 33 and extends from the shoulder arc 33 toward the sidewall15.

The sidewalls 15 are provided on the tire-radially inward of the treadportion 10 on the both edges of the pneumatic tire 1 in the tire widthdirection. Each of the two sidewalls 15 on the edges curves such thatthe sidewall 15 forms an arc in convex outward in the tire widthdirection in the meridian cross section of the sidewall 15. Furthermore,because each of the two sidewalls 15 on the edges curves such that thesidewall 15 forms the arc in convex outward in the tire width direction,the distance between two sidewalls 15 at positions outmost from theequatorial plane 5 in the tire width direction represents the totalwidth of the pneumatic tire 1.

The tread surface 11 of the pneumatic tire 1 is formed as descried in away that K1 obtained by Equation (11) below satisfies 0.6≦K1≦0.8, and K2obtained by Equation (12) below satisfies 0.9≦K1≦2.0. In Equations (11)and (12), L1 denotes an outline area representing a width between theequatorial plane 5 in the tire width direction and a center-arc end 35serving as the end of the center arc 31 in the tire width direction; ODdenotes the outside diameter of the pneumatic tire 1, that is, thediameter of the portion of the tread surface 11 having the largestradius in the tire-radial direction; and TDW denotes the treaddevelopment width that is the width of the tread surface 11 in the tirewidth direction. K1 obtained by Equation (11) represents the relationbetween the outline area L1 and the tread development width TDW. K2obtained by the following Equation (12) represents the ratio of thecurvature radius TR1 of the center arc 31 to the tire outside diameterOD.

K1=L1/(TDW×0.5)  (11)

K2=TR1/OD  (12)

FIG. 2 is a detailed view of a portion A in FIG. 1. The treaddevelopment width TDW is a distance between two virtual tread edges 47on both sides of the tread portion 10 in the tire width direction.Specifically, the virtual tread edge 47 is the intersection between anshoulder-side-arc extension 45 and a side-arc extension 46 in themeridian cross section of the pneumatic tire 1. The shoulder-side-arcextension 45 is a virtual line that extends from one of theshoulder-side arcs 32 on both sides of the pneumatic tire 1 in the tirewidth direction. The side-arc extension is a virtual line that extendsfrom the side arc 34 connected to the shoulder arc 33 formed to becontinuous from the shoulder-side arc 32. The virtual tread edges 47 areformed on both edge sides in the tire width direction, and the distancebetween the virtual tread edges 47 in the tire width direction isregarded as the tread development width TDW.

The pneumatic tire 1 is formed in a way that K3 obtained in accordancewith Equation (13) below satisfies 0.40≦K3≦0.48. In Equation (13), βdenotes the aspect ratio of the pneumatic tire 1, and SW denotes thetotal width of the pneumatic tire 1 in the tire width direction. K3represents the relation between the aspect ratio β, the treaddevelopment width TDW and the total width SW.

K3=(β×TDW)/(100×SW)  (13)

In the pneumatic tire 1, an angle α described below satisfies 35°≦α≦60°.The angle α is one of a plurality of angles formed by a center-arctangent 41 and a shoulder-arc tangent 42 when intersecting with eachother. The center-arc tangent 41 passes through the center-arc end 35and touches the center arc 31, and the shoulder-arc tangent 42 passesthrough a shoulder-arc end 36 that is an outward end of the shoulder arc33 in the tire width direction and touches the shoulder arc 33. Theangle α is positioned tire-radially inward from the center-arc tangent41 and outward from the shoulder-arc tangent 42 in the tire widthdirection.

The tread surface 11 of the pneumatic tire 1 is formed in a way that K4obtained by Equation (14) below satisfies 0.025≦K4≦0.035. K4 representsthe ratio of a curvature radius TR1 of the center arc 31 to a curvatureradius SHR of the shoulder arc 33.

K4=SHR/TR1  (14)

FIG. 3 is an explanatory view of a circumferential groove of thepneumatic tire shown in FIG. 1. The tread surface 11 of the treadportion 10 is provided with a plurality of circumferential grooves 50forming a tread pattern. The circumferential grooves 50 are formed alongthe tire circumferential direction, and the circumferential grooves 50are formed substantially in parallel in the tire width direction on thetread surface 11. The tread surface 11 is provided with a plurality ofribs 13 serving as land portions compartmentalized by thecircumferential grooves 50.

The circumferential grooves 50 on both edges of the pneumatic tire 1 inthe tire width direction among the circumferential grooves 50, or thecircumferential grooves 50 closest to the shoulders 16 among thosebetween the equatorial plane 5 and the shoulders 6, are shoulder-sidecircumferential grooves 51. The circumferential grooves 50 closest tothe equatorial plane 5 among those between the equatorial plane 5 andthe shoulders 6 are equatorial-plane-side circumferential grooves 55.

The positions of the shoulder-side circumferential groove 51 and theequatorial-plane-side circumferential groove 55 are described in detailbelow. The shoulder-side circumferential groove 51 is provided in theposition where T1 obtained in accordance with Equation (15) belowsatisfies 0.55≦T1≦0.65. In Equation (15), T1 represents the relationbetween the tread development width TDW and a distance H1 denoting adistance in the tire width direction between the equatorial plane 5 anda groove-width center 52 of the shoulder-side circumferential groove 51.

T1=H1/(TDW×0.5)  (15)

The equatorial-plane-side circumferential groove 55 is provided in theposition where T2 obtained in accordance with Equation (16) belowsatisfies 0.15≦T2≦0.20. In Equation (16), T2 represents the relationbetween a tread development width TDW and a distance H2 denoting adistance in the tire width direction between the equatorial plane 5 anda groove-width center 56 of the equatorial-plane-side circumferentialgroove 55.

T2=H1/(TDW×0.5)  (16)

The groove-width centers 52 and 56 are the centers of the openingsportions of the circumferential grooves 50 formed on the tread surface11 in the groove-width direction of the circumferential grooves 50.

When a vehicle in which the pneumatic tire 1 is installed travels, thepneumatic tire 1 rotates in a manner that the lower-positioned portionof the tread surface 11 is in contact with the road surface (not shown).Because the tread surface 11 is in contact with the road surface whilethe vehicle travels, a load resulting from the weight of the vehicle isapplied to the tread surface 11. The load applied to the tread surface11 changes depending on a traveling condition of the vehicle. Whencornering at a low speed, a relatively low load is applied to the treadsurface 11. By contrast, when changing a lane or cornering at a highspeed, a relatively high load is applied to the tread surface 11.

While the vehicle is traveling, the tread surface 11 is in contact withthe road surface as the applied load is changing as described above, andthe tread surface 11 deforms due to the applied load. Depending on thedeformation of the tread surface 11, the maximum value of the corneringforce, that is, the maximum cornering force, is changed in eachtraveling condition.

Specifically, when a low load is applied to the tread surface 11, thetread surface 11 tends not to deform. However, the tread surface 11 ofthe pneumatic tire 1 is designed to have the relation K1 between theoutline area L1 and the tread development width TDW to satisfy0.6≦K1≦0.8, and the ratio K2 of the curvature radius TR1 of the centerarc 31 to the tire outside diameter OD to satisfy 0.9≦K2≦2.0.Accordingly, a shape of the tread surface 11 at low load, for example,40% of the maximum load to be applied to the pneumatic tire 1, isapproximated to flat, so that a large contact area at low load isobtained.

In other words, by designing the ratio K2 of the curvature radius TR1 ofthe center arc 31 to the tire outside diameter OD to be 0.9 or more, thecurvature radius TR1 of the center arc 31 can be adequately large; andby setting K2 to 2.0 or less, an excessively large difference can beprevented between the curvature radiuses of the center arc 31 and theshoulder-side arc 32, and a large stress applied around the center-arcend 35 can be prevented.

When K1 representing the relation between the outline area L1 and atread development width TDW is 0.6 or more, the center arc 31 having thelarger curvature radius can be formed in a large area. When K1 is 0.8 orless, the area in which the shoulder-side arc 32 is formed can beassured and the curvature radius can gradually diminish from the centerarc 31 to the shoulder arc 33.

In this manner, the profile of the tread surface 11 can be approximatedto flat by designing K1 representing the relation between the outlinearea L1 and the tread development width TDW to satisfy 0.6≦K1≦0.8 and K2representing the ratio of the curvature radius TR1 to the tire outsidediameter OD to satisfy 0.9≦K2≦2.0. Consequently, the contact area underlow load, for example, 40% of the maximum load, can be increased, andthe maximum cornering force at low load can be increased. Accordingly,the driving stability during at low load can be increased. The maximumload includes “maximum load capacity” defined by JATMA, the maximumvalue described in “tire load limits at various cold inflation” definedby TRA, and “load capacity” defined by ETRTO.

When a high load is applied to the tread surface 11, the tread surface11 tends to deform. However, the contact area of the pneumatic tire 1 isnot so large when a high load is applied, because the pneumatic tire 1is formed in a way that K3 representing the relation between the aspectratio β, the tread development width TDW1, and the total width SWsatisfies 0.40≦K3≦0.48.

In other words, when K3 representing the relation between the aspectratio β, the tread development width TDW1, and the total width SW is0.40 or more, the tread development width TDW relative to the totalwidth SW of the pneumatic tire 1 can be smaller. When K3 is 0.48 orless, the minimum tread development width TDW relative to the totalwidth SW can be assured. Accordingly, an increase in the contact areaunder high load, for example, 100% of the maximum load of the pneumatictire 1 onto the tread surface 11, can be reduced, and the maximumcornering force at high load can be reduced. Hence, the rolloverresistance at high load can be improved. As a consequence, the rollovercharacteristics can be improved while retaining the driving stability.

Because the pneumatic tire 1 is formed in a way that the angle α formedby the center-arc tangent 41 and the shoulder-arc tangent 42 satisfies35°≦α≦60°, the rollover characteristics can be improved more reliably.

Specifically, by setting the angle α formed by the center-arc tangent 41and the shoulder-arc tangent 42 to 35° or larger, the angle near theshoulder 16 can be largely different from that of the tread surface 11,the shoulder 16 positioned between the tread surface 11 and the sidewall15. In other words, the shoulder 16 can drop at a steep angle. Moreover,by setting the angle α formed by the center-arc tangent 41 and theshoulder-arc tangent 42 to 60° or smaller, the rigidity around theshoulder arc 33 can be assured. The rigidity prevents a large portion ofthe shoulder 16 from contacting with the road surface due to deformationof the shoulder 16 under high load and a large slip angle, and preventsthe contact area from being increased because the shoulder 16 deformsand contacts with the road surface. Accordingly, the maximum corneringforce at high load can be reduced more reliably, and the rolloverresistance at high load can be improved more reliably. As a consequence,the rollover characteristics can be improved more reliably.

Because the pneumatic tire 1 is formed in a way that K4 representing theratio of the curvature radius TR1 of the center arc 31 to the curvatureradius SHR of the shoulder arc 33 satisfies 0.025≦K4≦0.035, the rollovercharacteristics can be improved more reliably. In other words, bysetting the ratio K4 of the curvature radius TR1 of the center arc 31 tothe curvature radius SHR of the shoulder arc 33 to 0.025 or more, therigidity near the shoulder arc 33 can be assured. On the other hand, bysetting K4 representing the ratio of the curvature radius TR1 of thecenter arc 31 to the curvature radius SHR of the shoulder arc 33 to0.035 or less, the shoulder 16 can have the large angle and be steep.The rigidity and the angle prevent a large portion of the shoulder 16from being in contact with the ground due to deformation of the shoulder16 under high load and a large slip angle, and prevent the contact areafrom being increased due to deformation of the shoulder 16. Accordingly,the maximum cornering force at high load can be reduced more securely,and the rollover resistance at high load can be improved more reliably.In consequence, the rollover characteristics can be improved morereliably.

Because the compound having the 300% tensile modulus of 5 MPa to 10 MPais used for the cap tread 12, a frictional force in the tire widthdirection at high load and a large slipping angle can be reduced and therollover resistance can be improved. In consequence, the rollovercharacteristics can be improved more reliably.

Because the anisotropic rubber having a 300% tensile modulus in the tirewidth direction smaller than that in the tire circumferential directionis used as the compound from which the cap tread 12 is made, therollover resistance can be improved. Specifically, the use of theanisotropic rubber as the compound of the cap tread 12 makes it possibleto reduce a frictional force in the tire width direction at high loadand a large slipping angle, thereby improving the rollover resistance.In consequence, the rollover characteristics can be improved morereliably.

The compound used for the cap tread 12 and having the 300% tensilemodulus of 5 MPa to 10 MPa can be used for a part of the cap tread 12 orfor the whole of the cap tread 12. Similarly, the anisotropic rubberused as the compound for forming the cap tread 12 and having the modulusin the tire width direction smaller than that in the tirecircumferential direction can be used for a part of the cap tread 12 orfor the whole of the cap tread 12. The use of the compound and theanisotropic rubber for at least a part of the cap tread 12 reduces thefrictional force in the tire width direction at high load and a largerslip angle, and improves the rollover characteristics more reliably.

The rollover characteristics can be improved and the driving stabilitycan be retained as well more reliably by providing the shoulder-sidecircumferential groove 51 in the position where T1 satisfies0.55≦T1≦0.65, T1 being calculated to represent the relation between thetread development width TDW and the distance H1 between the equatorialplane 5 and the groove-width center 52 of the shoulder-sidecircumferential groove 51 in the tire width direction. In other words,by setting the distance H1 between the equatorial plane 5 and thegroove-width center 52 of the shoulder-side circumferential groove 51 to55% of the half of the tread development width TDW or more, theshoulder-side circumferential grooves 51 is prevented from being tooclose to the equatorial plane 5 in the tire width direction.Accordingly, a decrease in the rigidity of the tread portion 10 in thevicinity of the center in the tire width direction, more specifically,the block rigidity which is the rigidity of the rib 13 formed on thetread portion 10, can be prevented, and the block rigidity in thevicinity of the center in the tire width direction is assured. Hence,the driving stability can be assured.

When the distance H1 between the equatorial plane 5 and the groove-widthcenter 52 of the shoulder-side circumferential groove 51 is 65% of thehalf of the tread development width TDW, the shoulder-sidecircumferential groove 51 is prevented from being too close to the outerside, that is, the shoulder 16 in the tire width direction.Consequently, a too high rigidity in the vicinity of the center in thetire width direction is prevented, so that too much increase in thecornering force at high load is prevented. Accordingly, the rollovercharacteristics can be improved more reliably. For this reason, byproviding the shoulder-side circumferential groove 51 in the positionwhere the relation T1 between the tread development width TDW and thedistance H1 between the equatorial plane 5 and the groove-width center52 of the shoulder-side circumferential groove 51 satisfies0.55≦T1≦0.65, the appropriate block rigidity in the vicinity of thecenter in the tire width direction can be achieved. In consequence, therollover characteristics can be improved and the driving stability canbe retained as well more reliably.

The driving stability can be assured more reliably because theequatorial-plane-side circumferential groove 55 is provided in theposition where T2 satisfies 0.15≦T2≦0.20, T2 being calculated torepresent the relation between the tread development width TDW and thedistance H2 between the equatorial plane 5 and the groove-width center56 of the equatorial-plane-side circumferential groove 55. Specifically,by setting the distance H2 between the equatorial plane 5 and thegroove-width center 56 of the equatorial-plane-side circumferentialgroove 55 to 15% of the half of the tread development width TDW or more,the equatorial-plane-side circumferential groove 55 can be preventedfrom being too close to the equatorial plane 5 in the tire widthdirection. Consequently, a too low rigidity in the vicinity of thecenter in the tire width direction can be prevented, and a response ofthe pneumatic tire 1 when cornering can be assured.

When the distance H2 between the equatorial plane 5 and the groove-widthcenter 56 of the equatorial-plane-side circumferential groove 55 is 20%of the half of the tread development width TDW or less, theequatorial-plane-side circumferential groove 55 can be prevented frombeing too close to the shoulder 16 in the tire width direction.Accordingly, a too high rigidity in the vicinity of the center in thetire width direction is suppressed, and a too quick response of thepneumatic tire 1 when cornering is avoided. For this reason, the blockrigidity in the vicinity of the center in the tire width direction canbe appropriate by providing the equatorial-plane-side circumferentialgroove 55 in the position where the relation T2 between the treaddevelopment width TDW and the distance H2 between the equatorial plane 5and the groove-width center 56 of the equatorial-plane-sidecircumferential groove 55 satisfies 0.15≦T2≦0.20. Because of therigidity, the response of the pneumatic tire 1 when cornering can beappropriate and the driving stability can be assured more reliably.

The number of the circumferential grooves 50 does not matter as long asa plurality of the circumferential grooves 50 is provided on the treadsurface 11. The rollover characteristics can be improved more reliablywhile the driving stability can be retained by forming the shoulder-sidecircumferential groove 51 among the circumferential grooves 50, which isclosest to the shoulder 16 between the equatorial plane 5 and theshoulder 16, in the position where T1 is in the above range, T1representing the relation between the tread development width TDW andthe distance H1 between the shoulder-side circumferential groove 51 andthe equatorial plane 5. The driving stability can be improved morereliably by forming the equatorial-plane-side circumferential groove 55among the circumferential grooves 50, which is closest to the equatorialplane 5 between the equatorial plane 5 and the shoulder 16, in theposition where T2 is in the above range, T2 representing the relationbetween the tread development width TDW and the distance H2 between theequatorial-plane-side circumferential groove 55 and the equatorial plane5.

FIG. 4 is a modified example of the pneumatic tire according to theembodiment and is a view that depicts the tread. The circumferentialgrooves 50 can be formed not in the precise tire circumferentialdirection. It suffices that the circumferential grooves 50 are formedapproximately in the tire circumferential direction and can be formed inthe direction diagonal to the tire width direction or can be formedalong a curved line or in zigzag. In such a case where thecircumferential groove 50 is formed as extending in the tirecircumferential direction while extending inward and outward repeatedlyin the tire width direction between the edges of the circumferentialgroove 50, it suffices that the position of the circumferential groove50 is determined by determining the center between the edges of thecircumferential groove 50 in the tire width direction as thegroove-width center.

For example, as shown in FIG. 4, when the circumferential groove 50 isformed in zigzag, it suffices that the centerline between virtual linespassing through the respective edges of the circumferential groove 50 inthe tire circumferential direction is determined as the groove-widthcenter. Specifically, when the shoulder-side circumferential groove 51is formed in zigzag, the centerline between a groove-width-directionedge line 53 at the side of the shoulder 16 and thegroove-width-direction edge line 53 at the side of the equatorial plane5 in the tire width direction can be the groove-width center 52 of theshoulder-side circumferential groove 51. Accordingly, when theshoulder-side circumferential groove 51 is formed in zigzag, it sufficesthat the distance between the groove-width center 52 and the equatorialplane 5 is determined as H1 and that the shoulder-side circumferentialgroove 51 is formed in the position where the relation T1 between H1 andthe tread development width TDW suffices 0.55≦T1≦0.65. Similarly, whenthe equatorial-plane-side circumferential groove 55 is formed in zigzag,it suffices that the centerline between a groove-width-direction edgeline 57 at the side of the shoulder 16 and the groove-width-directionedge line 57 at the side of the equatorial plane 5 in the tire widthdirection is determined as the groove-width center 56 of theequatorial-plane-side circumferential groove 55. Accordingly, when theequatorial-plane-side circumferential groove 55 is formed in zigzag, itsuffices the distance between the groove-width center 56 and theequatorial plane 5 is determined as H2 and that theequatorial-plane-side circumferential groove 55 is formed in theposition where the relation T2 between H2 and the tread developmentwidth TDW suffices 0.15≦T2≦0.20.

FIG. 5 is an explanatory view of the tread and the bead filler of thepneumatic tire shown in FIG. 1. In many cases, the tread portion 10 isformed of a tread rubber 60 including, in addition to the cap tread 12,a base rubber ply 61 and wing chips 62 that are made from rubberdifferent from that for forming the cap tread 12. It is preferable thatthe properties of the tread portion 10 and the ratio of the base rubberply 61 to the tread rubber 60 be defined in a predetermined range.Specifically, as shown in FIG. 5, the tread portion 10 is generallyformed of the tread rubber 60 including the cap tread 12, the baserubber ply 61 at the tire-radially inward of the cap tread 12, and thewing chip 62 on each of both sides of the cap tread 12 in the tire widthdirection. It is preferable that the base rubber ply 61 be formed sothat the cross-sectional area of the base rubber ply 61 in the meridiancross section of the tread rubber 60 is 20% to 50% of thecross-sectional area of the tread rubber 60. In addition, the baserubber ply 61 preferably has a JIS-A hardness (JIS K6253) of 48 to 60 atroom temperature, specifically, at 20° C.

In many cases, the cap tread 12 has a JIS-A hardness (JIS K6253) ofabout 64 to 72. For this reason, by forming the base rubber ply 61having a JIS-A hardness of 48 to 60 at room temperature, the hardness ofthe base rubber ply 61 to that of the cap tread 12 can be lowered morereliably. Furthermore, by forming the base rubber ply 61 in a way thatthe cross-sectional area of the base rubber ply 61 in the meridian crosssection of the tread rubber 60 is 20% to 50% of the cross-sectional areaof the tread rubber 60, the maximum cornering force at high load can bedecreased more reliably and the maximum cornering force at low load canbe increased.

Specifically, by designing the cross-sectional area of the base rubberply 61 with a lower hardness to be 20% of that of the tread rubber 60 orlarger, the base rubber ply 61 having the lower hardness can have alarge thickness. The thickness decreases the rigidity of the entiretread rubber 60, in other words, the rigidity of the entire treadportion 10. Accordingly, the maximum cornering force at high load can bereduced and the rollover resistance at high load can be improved.Because of the decrease in the rigidity of the entire tread portion 10,the rollover resistance at high load can be improved and thus the gripperformance at low load can be improved. Hence, because the rubber thatachieves higher grip performance can be used for the cap tread 12 toobtain the maximum cornering force at low load, the driving stabilityand the braking performance at low load can be improved.

By designing the cross-sectional area of the base rubber ply 61 having alower hardness to be 50% of that of the tread rubber 60 or less, anexcessive thickness of the base rubber ply 61 of the lower hardnessrubber can be suppressed, and hence the rigidity of the entire treadportion 10 can be prevented from being too low. The rigidity preventsthe maximum cornering force at low load from being too low, therebyassuring the driving stability and the control performance at low load.For this reason, by forming the base rubber ply 61 as described above,the maximum cornering force at high load can be decreased more securelywhile the maximum cornering force at low load can be increased. Inconsequence, the rollover characteristics can be improved whileretaining the driving stability more reliably.

It is preferable that the bead filler 26 be formed in a way that Gobtained by Equation (17) below satisfies 6≦G≦11. Specifically, inEquation (17), Hs denotes the JIS-A hardness (JIS K6253) of the beadfiller 26 at room temperature, and FH(mm) denotes a filler height whichis the distance between an outward edge 27 and an inner-side inward edge28. The outward edge 27 is the tire-radially outermost point in themeridian cross section of the bead filler 26, and the inner-side inwardedge 28 is an edge on the inner side in the tire width direction fromamong edges on the tire-radially inward of the bead filler 26. In otherwords, the filler height is the distance between the outward edge 27 andthe inner-side inward edge 28 that is the farthest point from theoutward edge 27. In this case, it is preferable that the pneumatic tire1 according to the present invention be formed in a way that G obtainedby Equation (17) below satisfies 6≦G≦11, more preferably, 7≦G≦9.Equation (17) is the relation between the JIS-A hardness Hs of the beadfiller 26 at room temperature, the filler height FH, the tire outsidediameter OD, and the aspect ratio β.

G=(Hs×FH)/(OD×β)  (17)

The rigidity of the bead filler 26 can be appropriate by providing thebead filler 26 in a way that G satisfies 6G≦≦11, G being calculated torepresent the relation between the JIS-A hardness Hs of the bead filler26, the filler height FH, the tire outside diameter OD, and the aspectratio β. In other words, by forming the bead filler 26 in a way that Gis 6 or larger, the hardness Hs of the bead filler 26 can be preventedfrom being too low or the filler height FH from being too small.Accordingly, the rigidity of the bead filler 26 is assured and thus therigidity the sidewall 15 can be assured. Hence, the maximum corneringforce at low load can be assured more reliably.

By forming the bead filler 26 in a way that G is 11 or smaller, thehardness Hs of the bead filler 26 can be prevented from being too highor the filler height FH from being too large. Accordingly, the rigidityof the bead filler 26 can be prevented from being too high and thus therigidity of the sidewall 15 can be prevented from being too high. Hence,the maximum cornering force at high load can be reduced more reliably.For this reason, the rigidity of the bead filler 26 can be appropriateby providing the bead filler 26 in a way that the relation between theJIS-A hardness Hs of the bead filler 26 at room temperature, the fillerheight FH of the bead filler, the tire outside diameter OD, and theaspect ratio β satisfies 6≦G≦11. Because of the appropriate rigidity,the driving stability at low load can be assured more reliably and themaximum cornering force at high load can be reduced. In consequence, therollover characteristics can be improved more reliably while the drivingstability can be retained. Furthermore, when the bead filler 26 isprovided in a way that relation between the JIS-A hardness Hs of thebead filler 26 at room temperature, the filler height FH of the beadfiller, the tire outside diameter OD, and the aspect ratio β satisfies7≦G≦9, both of the driving stability and the rollover characteristicscan be improved.

Although the filler height FH denotes the distance between the outwardedge 27 and the inner-side inward edge 28, the filler height FH candenote a different distance. For example, FH can denote the distancebetween the outward edge 27 of the bead filler 26 and an outer-sideinward edge 29 that is an edge on the outer side in the tire widthdirection on from among the edges of the bead filler 26 on thetire-radially inward. It suffices that the filler height FH is the widthof a portion of the bead filler 26 having the largest width in the beadfiller 26 in the direction approximately along the sidewall 15 or thecarcass 22. The filler height FH can be a distance other than thedistance between the outward edge 27 and the inner-side inward edge 28.

FIG. 6 is an explanatory view that depicts a modified example of thepneumatic tire according to the embodiment. The shape of the base rubberply 61 is not a problem as long as the base rubber ply 61 is formed in away that the cross-sectional area of the base rubber ply 61 in the crosssection of the tread rubber 60 is 20% to 50% of that of the tread rubber60. For example, as shown in FIG. 5, the base rubber ply 61 can beformed approximately along the belt ply 21 and have an approximatelyeven thickness in the tire-radial direction. Alternatively, as shown inFIG. 6, the base rubber ply 61 can be formed in a way that a portionclose to the shoulder 16 is thicker than a portion close to theequatorial plane 5. The shape of the base rubber ply 61 is not a problemas long as the JIS-A hardness is between 48 and 60 and thecross-sectional area of the base rubber ply 61 in the meridian crosssection of the tread rubber 60 is 20% to 50% of the cross-sectional areaof the tread rubber 60. By forming the base rubber ply 61 in the abovemanner, the driving stability can be retained more reliably while therollover characteristics can be improved.

FIG. 7 is an explanatory view that depicts a modified example of thepneumatic tire according to the embodiment. The arcs in the crosssection of the tread portion 10 of the present invention are notnecessarily formed on each of both sides in the tire width direction asdescribed and can be formed as described on only tire widthdirection-vehicle-outer side. Specifically, the outline area on thevehicle-outer side in the tire width direction can be different fromthat on the vehicle inner side in the tire width direction, and theoutline area L1 can be the outline area on the vehicle-outer side in thetire width direction. In this case, K1 obtained by the above Equation(1) represents the relation between the tread development width TDW andthe outline area L1 on the vehicle-outer side in the tire widthdirection and satisfies 0.6≦K1≦0.8. In this case, L1 _(in) denotes theoutline area on the vehicle inner side in the tire width direction andis smaller than the outline area L1 on the vehicle-outer side in thetire width direction. The tread portion 10 is formed in a way that therelation K1 _(in) between the outline area L1 _(in) and the treaddevelopment width TDW satisfies 0.4≦K1 _(in)≦0.6, K1 _(in) beingcalculated by Equation (18) below. It is preferable that K1 _(in)satisfy 0.5≦K1 _(in)≦0.56. More preferably, K1 _(in) and K1 satisfiesthe relation indicated by K1 _(in)≦K1×0.9.

K1_(in) =L1_(in)/(TDW×0.5)  (18)

By forming the arcs in a way that the outline area on the vehicle-outerside in the tire width direction is different from that on the vehicleinner side in the tire width direction, and that the relation K1 _(in)between the tread development width TDW and the outline area L1 _(in) onthe vehicle inner side in the tire width direction satisfies 0.4≦K1_(in)≦0.6 as described, the outline area on the vehicle inner side inthe tire width direction can be smaller. The outline area on the vehicleinner side in the tire width direction can be smaller more reliably whenthe relation K1 _(in) between tread development width TDW and theoutline area L1 _(in) on the vehicle inner side in the tire widthdirection is 0.9 times or smaller than the relation K1 between the treaddevelopment width TDW and the outline area L1 on the vehicle-outer sidein the tire width direction. As a result, compared with the treadsurface 11 on the vehicle-outer side in the tire width direction, thetread surface 11 on the vehicle inner side in the tire width directionincludes a wider area in which the shoulder-side arc 32 and the shoulderarc 33 are formed. The area increases the contact width when thevicinity of the shoulder 16 on the vehicle inner side in the tire widthdirection is in contact with the road surface during, for example,cornering, thereby preventing the contact pressure from being too highand the wear resulting from a too high contact pressure. For example,when a negative camber angle is defined, the tread surface 11 on thevehicle inner side in the tire width direction tends to be in contactwith the road surface. However, the wear of the tread surface on thevehicle inner side in the tire width direction is prevented in the abovecase because the contact pressure of the tread surface 11 on the vehicleinner side in the tire width direction tends not to be higher. In thismanner, the wear of the shoulder on the vehicle inner side in the tirewidth direction can be prevented from occurring. On the other hand, whenthe vicinity of the shoulder 16 on the vehicle inner side in the tirewidth direction is in contact with the road surface, the rollovercharacteristics can be improved. In consequence, the rollovercharacteristics and the wear resistance can be improved.

When K1 _(in) satisfying 0.4≦K1 _(in)≦0.6, the maximum cornering forceat low load can be assured, while the contact pressure, which is appliedwhen the vicinity of the shoulder 16 on the vehicle inner side in thetire width direction is in contact with the road surface, can bereduced. Specifically, when K1 _(in) is 0.4 or larger, the outline areaL1 _(in) on the vehicle inner side in the tire width direction can be acertain value and thus the maximum cornering force at low load can beassured. When K1 _(in) is 0.6 or smaller, the outline area L1 _(in) onthe vehicle inner side in the tire width direction can be smaller morereliably and thus the contact pressure, which is applied when thevicinity of the shoulder 16 on the vehicle inner side in the tire widthdirection is in contact with the road surface, can be reduced morereliably. For this reason, when K1 _(in) representing the relationbetween tread development width TDW and the outline area L1 _(in) on thevehicle inner side in the tire width direction satisfies 0.4≦K1_(in)≦0.6, the maximum cornering force at low load can be assured andthe contact pressure, which is applied when the vicinity of the shoulder16 on the vehicle inner side in the tire width direction is in contactwith the road surface, can be reduced as well. In consequence, therollover characteristics and the wear resistance can be improved.

FIG. 8 is an explanatory view that depicts a modified example of thepneumatic tire according to the embodiment. When a belt cover ply 70 isprovided to the belt ply 21 on the outer side in the tire widthdirection, the rigidity of reinforcing cords 75, which are included inthe belt cover ply 70 in the vicinity of the center in the tire widthdirection, can be different from that in the vicinity of the shoulder16. For example, as shown in FIG. 8, the belt cover ply 70 can beprovided to the belt ply 21 on the tire-radially outward in a way thatthe belt ply 21 covers the belt ply 21 and the tensile force of acentral region 71 at the center of the belt cover ply 70 in tire widthdirection is different from that of a shoulder region 72 on each of bothsides of the central region 71 in the tire width direction.

Specifically, the belt cover ply 70 is provided in a way that the ratioof a cover-tensile-force index Ec of the central region 71 of the beltcover ply 70 to a cover-tensile-force index Es of the shoulder region 72of the belt cover ply 70 satisfies 1.0<Es/Ec. The cover-tensile-forceindex Ec is obtained by Equation (19) below. In Equation (19), Dcdenotes the end count of central-region reinforcing cords 76 that arethe reinforcing cords 75 provided to the central region 71 of the beltcover ply 70, that is, the number of the central-region reinforcingcords 76 per 50 mm in the direction in which the central-regionreinforcing cords 76 are arranged, and Sc denotes an elongation of oneof the central-region reinforcing cords 76 to which a load of 50N isapplied. The elongation of the reinforcing cord 75 is measured accordingto the tensile test method described in JIS L1007, using the reinforcingcord 75 sampled from the belt cover ply 70 of the pneumatic tire 1.

Ec=Dc/Sc  (19)

The cover-tensile-force index Es is obtained by Equation (20) below. InEquation (20), Ds denotes the end count of shoulder-region reinforcingcords 77 that are the reinforcing cords 75 provided to the shoulderregion 72 of the belt cover ply 70, that is, the number of theshoulder-region reinforcing cords 77 per 50 nm in the direction in whichthe shoulder-region reinforcing cords 77 are arranged, and Ss denotes anelongation of one of the shoulder-region reinforcing cords 77 to which aload of 50N is applied.

Ec=Ds/Ss  (20)

It is preferable that the belt cover ply 70 be formed in a way that thecover-tensile-force index Es of the shoulder region 72 of is larger thanthe cover-tensile-force index Ec of the central region 71, and morepreferably, the cover-tensile-force index Ec of the central region 71and the cover-tensile-force index Es of the shoulder region 72 satisfy1.2<Es/Ec<4.

When the belt cover ply 70 is formed in a way that thecover-tensile-force index Es of the shoulder region 72 is larger thanthe cover-tensile-force index Ec of the central region 7, for example,the number of the reinforcing cords 75 in the shoulder region 72 can belarger than that in the central region 71. Alternatively, a tensileforce larger than that applied to the central-region reinforcing cords76 can be applied to the shoulder-region reinforcing cords 77 during itsprovision so that the initial tensile force of the shoulder-regionreinforcing cords 77 is larger than that of the initial tensile force ofthe central-region reinforcing cords 76. Alternatively, the belt coverply 70 cab be provided to only the vicinity of the shoulder 16 or thenumber of the belt cover ply 70 near the shoulder 16 can be larger thanthat near the equatorial plane 5.

By forming the belt cover ply 70 in a way that the ratio of thecover-tensile-force index Ec of the central region 71 to thecover-tensile-force index Es of the shoulder region 72 satisfies1.0<Es/Ec as described, change in contact length of the tread surface 11in the vicinity of the shoulder 16 can be smaller when the tread surface11 in the vicinity of the shoulder 16 is in contact with the roadsurface. In other words, when ES/EC is 1.0 or larger, specifically, whenthe cover-tensile-force index Es of the shoulder region 72 is largerthan the cover-tensile-force index Ec of the central region 71, therigidity of the shoulder region 72 of the belt cover ply 70 can belarger than that of the central region 71 of the belt cover ply 70.Accordingly, the contact length of the shoulder 16 under high load and alarge slop angle can be smaller or the change of the contact length canbe prevented. Hence, the maximum cornering force at high load can bereduced more reliably.

In this manner, by forming the belt cover ply 70 in a way that the ratioof the cover-tensile-force index Ec of the central region 71 to thecover-tensile-force index Es of the shoulder region 72 satisfies10.0<Es/Ec, the cover-tensile-force index Es of the shoulder region 72can be securely larger than the cover-tensile-force index Ec of thecentral region 71 and thus the contact length of the shoulder 16 underhigh load and a large slop angle can be smaller or the change of thecontact length can be prevented. In consequence, the maximum corneringforce at high load can be reduced, and hence the rollovercharacteristics can be improved more reliably.

FIG. 9 is an explanatory view that depicts a modified example of thepneumatic tire according to the embodiment. FIG. 10 is a view viewedfrom an arrow-headed line B-B in FIG. 9. When a lug groove 80 isprovided to the tread surface 11 in the shoulder 16, a recess can beprovided to the lug groove 80 to reduce the maximum cornering force athigh load. For example, when the lug groove 80 is formed on the treadsurface 11 in the shoulder 16 as shown in FIG. 9, a recess 85 can beprovided in the lug groove 80 in the vicinity of the shoulder 16. Therecess 85 forms a recess at a groove bottom 81 of the lug groove 80, andis on the outer side in the tire width direction of a contact end 90 ofthe pneumatic tire 1. The lug grooves 80 are formed in order in the tirecircumferential direction, and the recess 85 is provided to each of thelug grooves 80 of the shoulder 16. The recess 85 forms a rectanglehaving the width in the groove-width direction of the lug groove 80slightly narrower than the groove width of the lug groove 80 (FIG. 10).Because the lug groove 80 is thus formed in the vicinity of the shoulder16, at least land portions in the vicinity of the shoulder 16 serve asblock portions 83 compartmentalized by the lug grooves 80 and thecircumferential grooves 50.

The contact end 90 of the pneumatic tire 1 is an edge of the face of thepneumatic tire 1 in the tire width direction that is mounted on theregular rim and to which the regular inner pressure is applied and thena regular load is applied, the pneumatic tire 1 is keeping still andbeing perpendicular to a plate, and the face being in contact with theplate. The regular load includes the “maximum load resistance” definedby JATMA, the maximum value of the “tire load limits at various coldinflation pressures” defined by TRA and “load capacity” defined byETRTO. In the case of a pneumatic tire for passenger cars, the standardload is 88% of the maximum load capacity.

Because the recess 85 is formed at the groove bottom 81 of the luggroove 80 and is on the outer side of the contact end 90 in the tirewidth direction, the rigidity of the block portions 83 in a region onthe outer side of the contact end 90 in the tire width direction(rigidity in the shear direction), in other words, the region notcontacting with the road surface in a normal driving mode, can bereduced. Accordingly, the block portions 83 having the lower rigiditycan be in contact with the road surface when the region on the outerside of the contact end 90 in the tire width direction is in contactwith the road surface under high load and a large slip angle because of,for example, cornering. In this manner, the maximum cornering force athigh load can be reduced more reliably. The recess 85 is on the outerside of the contact end 90 in the tire width direction, and the regionon the outer side of the contact end 90 in the tire width direction isin contact with the road surface in the normal driving mode. Because theregion to which the recesses 85 are provided is not in contact with theroad surface in the normal driving mode, for example, at low load, therecesses 85 cause no influence and the maximum cornering force at lowload can be assured. Accordingly, the driving stability at low load canbe assured. In consequence, the rollover characteristics can be improvedwhile the driving stability can be retained more reliably.

Because the rigidity of the block portion 83 in the vicinity of theshoulder 16 can be reduced because of the recess 85 formed in the luggroove 80 in the shoulder 16, the block portion 83 tends to deform whenthe block portion 83 is in contact with the road surface. Accordingly, aload applied to the tread surface 11 in the block portion 83 can bedispersed and received by the tread surface 11 and a too high contactpressure can be prevented. Hence, the wear resulting from a too highcontact pressure in the vicinity of the shoulder 16 can be prevented. Inconsequence, the shoulder wear can be prevented.

FIG. 11 is a detailed view of a portion C shown in FIG. 9. It ispreferable that the recess 85 is formed in the lug groove 80 in theshoulder 16 in a way that a depth H of the deepest portion of the recess85 and an average D (=D1+D2/2) between groove depths D1 and D2 at bothends of the recess 85 in the tire width direction, in other words, inthe groove-length direction of the lug groove 80, satisfy 0.20≦H/D≦0.50.When 0.20≦H/D≦0.50 is satisfied, the rigidity of the block portions 83can be reduced and the thickness of the tread rubber 60 in the shoulder16 can be assured as well. For example, when H/D≦0.20 is satisfied,there is a risk that the rigidity of the block portions 83 cannot beeffectively reduced and thus it is difficult to obtain the effect of theimprovement in the rollover characteristics resulting from the provisionof the recess 85. Meanwhile, when 0.50≦H/D is satisfied, there is a riskthat the thickness of the tread rubber 60 is insufficient in theshoulder 16 and thus the durability of the pneumatic tire 1 isdecreased. For this reason, by forming the recess 85 in a way that thedepth H of the deepest portion of the recess 85 and the average Dbetween the groove depths D1 and D2 at both ends of the recess 85satisfy 0.20≦H/D≦0.50, the thickness of the tread rubber 60 in theshoulder 16 can be assured while the rigidity of the block portion 83can be reduced. Hence, the rollover characteristics can be improved morereliably and the durability can be improved. The depth H of the deepestportion of the recess 85 is determined based on the groove bottom 81 ofthe lug groove 80, and the position of the deepest portion of the recess85 is not particularly limited.

The recess 85 is preferably between the contact end 90 of the treadportion 10 and a limit contact end 91 (see FIGS. 10 and 11).Accordingly, the driving stability and the durability can be bothachieved. Specifically, when the recess 85 is on the inner side of thecontact end 90 of the tread portion 10 in the tire width direction,there is the risk that the rigidity of the block portion 83 in thevicinity of the recess 85 decreases and thus the maximum cornering forceat low load is reduced and thus the driving stability decreases.Meanwhile, when the recess 85 is on the outer side of the limit contactend 91 of the tread portion 10 in the tire width direction, there is arisk that the rigidity in the vicinity of the shoulder 16 isinsufficient and thus the durability of the pneumatic tire 1 decreases.For this reason, both of the driving stability and the durability can beimproved when the recess 85 is between the contact end 90 of the treadportion 10 and the limit contact end 91 of the tread portion 10.

The limit contact end 91 is a point that defines the distance from thecenter of the contact width of the pneumatic tire 1, the distance being1.3 times that between the center and the contact end 90. The contactwidth of the tire is the maximum linear distance in the tire widthdirection of the face of the pneumatic tire 1 mounted on the regular rimto which the regular inner pressure is applied and then a regular loadis applied, the pneumatic tire 1 keeping still and being perpendicularto a plate, and the face being in contact with the plate.

FIG. 12 is an explanatory view of the recess formed in a tapering shape,and is a cross sectional view along the line D-D in FIG. 10. FIG. 13 isan explanatory view of the recess formed in a tapering shape, and is across sectional view along the line E-E in FIG. 10. FIG. 14 is anexplanatory view of the recess that forms a curved surface, and is across sectional view along the line D-D in FIG. 10. FIG. 15 is anexplanatory view of the recess that forms a curved surface, and is across sectional view along the line E-E in FIG. 10. It is preferable therecess 85 is formed in the lug groove 80 in the shoulder 16 in a waythat the opening area of the recess 85 gradually diminishes from theopening plane to the deepest portion of the recess 85. For example, asshown in FIGS. 12 and 13, the recess 85 can be formed in a way that asidewall 86 of the recess 85 forms a tapering shape and the opening areaof the recess 85 gradually diminishes from the opening plane to thedeepest portion of the recess 85. Alternatively, as shown in FIGS. 14and 15, the recess 85 can be formed in a way that the recess 85 forms acurved surface and the opening area of the recess 85 graduallydiminishes from the opening plane to the deepest portion of the recess85. Such formation makes it easier to form the recess 85 because atire-forming mold can be easily removed from the recess 85 when thepneumatic tire 1 is formed. The recesses 85 can be symmetrical orasymmetrical in the groove-length direction of the lug groove 80.

FIG. 16 is an explanatory view that depicts a modified example of therecess and is a cross sectional view along the line B-B of FIG. 9. FIG.17 is an explanatory view that depicts a modified example of the recess,and is a cross sectional view along the line E-E of FIG. 10. FIG. 18 isan explanatory view that depicts a modified example of the recess, andis a cross sectional view along the line E-E of FIG. 10. Although therecess 85 is formed in the lug groove 80 in the shoulder 16 in a waythat the recess 85 has a cross sectional area extending approximately ina certain range toward the tire-width-outward direction (see FIG. 11),the recess 85 can be formed in a different shape. Specifically, therecesses 85 can be formed in any form although the recess 85 forms theapproximate rectangle along the groove width of the lug groove 80 in theplan view of the tread portion 10 and has the approximately uniformdepth H.

For example, the recess 85 can be formed in a way that thecross-sectional area of the recess 85 gradually increases as it extendsoutwardly in the tire width direction. For example, as shown in FIG. 16,when looking from the top, the recess 85 can be formed in a way that thewidth of the recess 85 in the groove-width direction of the lug groove80 at the end on the outer side in the tire width direction is largerthan that on the inner side in the tire width direction and thus asubstantial trapezoid is formed and that the opening width of the recess85 gradually increases as it extends outwardly in the tire widthdirection. Alternatively, as shown in FIGS. 17 and 18, the recess 85 canbe formed in a way that the depth H of the recess 85 gradually increasesas it extends outwardly in the tire width direction. By forming therecess 85 into any of the above shapes, the rigidity of the blockportion 83 in the vicinity of the recess 85 can be gradually diminishedas it extends outwardly in the tire width direction. Hence, the drivingstability can be retained at a large slip angle, as compared with astructure in which the rigidity of the block portion 83 drops from thevicinity of the contact end 90. In consequence, the driving stabilitycan be retained and the rollover characteristics can be improved aswell.

The recess 85 can form a rectangle in a plan view of the tread portion10 as described (see FIG. 10), or can form a circle or an ellipse (notshown). The shape of the recess 85 can be freely selected based on theshape of the lug groove 80 within the obvious scope of a person skilledin the art.

When the aspect ratio of the pneumatic tire 1 is 65% or smaller, theeffect is increased. The pneumatic tire 1 having the aspect ratio of 65%or smaller has a higher rigidity to a load applied to the tread surface11 in the tire width direction, and thus, the cornering force tends tobe large at high load. For this reason, the pneumatic tire 1 having theaspect ratio of 65% or smaller tends to have lower rollover resistance.However, by designing the tread surface 11 of the pneumatic tire 1 tohave the profile in the above-described shape, the rollovercharacteristics can be improved as while retaining the driving stabilitymore effectively.

Although only the circumferential grooves 50 are provided in the tirecircumferential direction as the grooves formed on the tread surface 11of the pneumatic tire 1, any groove other than the circumferentialgrooves 50 can be formed. When grooves other than the circumferentialgrooves 50 are formed, it suffices that the tread surface 11 has theprofile in the above-described shape. Even when the circumferentialgrooves 50 are formed, a different groove such as a groove extending inthe tire width direction can be formed. In other words, although thepneumatic tire 1 has the tread pattern that is the rib pattern obtainedproviding only the circumferential grooves 50 to the tread surface 11,the pneumatic tire 1 can have any tread pattern such as the rib-lugpattern and the block pattern.

EXAMPLES

Evaluation tests of performance of the pneumatic tire 1, which wereconducted on conventional pneumatic tires and the pneumatic tires 1according to the present invention, are explained below. Sevenperformance evaluation tests were carried out. The two performanceevaluation tests of them were carried out by conducting only the doublelane change test, and the other five performance evaluation tests werecarried out by conducting the double lane change test and running anactual vehicle in a test course.

The first test method from among the seven performance evaluation testswas carried out by conducting a test run with a sport utility vehicle(SUV) having 1800 cc of displacement fitted with the pneumatic tires 1in the size of 225/65R17 that were mounted on the rims. As an evaluationmethod for the performance evaluation test, the double lane change test(elk test), which is defined in ISO 3888-2, was conducted with thevehicle described above, and the rollover characteristics weredetermined in accordance with whether wheels of the vehicle werelift-up. According to the determination, a case if the wheels were notlift-up was marked as successful, while the other case if the wheelswere lift-up was marked as failure. If the determination was successful,it was determined that the rollover characteristics were good.

As the pneumatic tires 1 to be examined with the test, two models oftires according to the present invention, three models of tires ascomparative examples to compare with the present invention, and onemodel of tires as a conventional example were tested by the first testmethod. The evaluation tests were conducted by the first test method onthe pneumatic tires 1 according to a conventional example 1, comparativeexamples 1 to 3, and present inventions 1 and 2, and obtained resultsare shown in FIG. 19.

The pneumatic tires 1 on which the evaluation tests by the first testmethod were conducted were all capable to perform a double lane changein the double lane change test, so that all of them retained the drivingstability. On the other hand, as stated in the results of the testsshown in FIG. 19, if K1, K2, K3, and K4 do not satisfy (0.6≦K1≦0.8),(0.9≦K2≦2.0), (0.40≦K3≦0.48), and (0.025≦K4≦0.035), respectively, therollover characteristics cannot be improved effectively (comparativeexamples 1 to 3).

By contrast, according to the present inventions 1 and 2, K1, K2, K3,and K4 are configured to satisfy (0.6≦K1≦0.8), (0.9≦K2≦2.0),(0.40≦K3≦0.48), and (0.025≦K4≦0.035), respectively. Accordingly, thedriving stability at low load, such as 40% of the maximum load, can beassured, and the maximum cornering force at high load, such as 70% to100% of the maximum load, can be reduced, so that the rolloverresistance at high load can be improved. Consequently, while retainingthe driving stability, the rollover characteristics can be improved.

The second test method from among the seven performance evaluation testswas carried out by conducting a test run with a vehicle having 1300 ccof displacement fitted with the pneumatic tires 1 in the size of185/60R15 that were mounted on the rims. As an evaluation method for theperformance evaluation test, similarly to the performance evaluationtest by the first test method, the double lane change test, which isdefined in ISO 3888-2, was conducted with the vehicle fitted with thepneumatic tires 1, and the rollover characteristics were determined inaccordance with whether wheels of the vehicle were lift-up. According tothe determination, a case if the wheels were lift-up was marked asfailure; a case if the wheels were not lift-up at a test speed of 60km/h was marked as successful; and a case if the wheels were not lift-upat a test speed of 62 km/h was marked as more successful; so that whenthe determination was successful or more successful, it was determinedthat the rollover characteristics were good. Moreover, in the evaluationmethod, the case where the wheels that are not lift-up at a higher speedcan be determined as better in the rollover characteristics. Therefore,it was determined that the case resulting in the determination moresuccessful was better in the rollover characteristics than the caseresulting in the determination successful.

In the performance evaluation test by the second test method, a test ofthe driving stability was also conducted. As a test method for thedriving stability, the vehicle ran at 60 km/h to 100 km/h through a testcourse that had a flat round route, and three specialized panelistsconducted sensory evaluations on steerage when changing a lane andcornering and stability when going straight. Evaluation results areindicated in indexes based on the evaluation result of the pneumatictire 1 according to a conventional example 2 set at 100, where thelarger index expresses the better driving stability. In the evaluationtest of the driving stability, if the index is at 96 or higher, it isdetermined that the steerage when changing a lane and cornering and thestability when going straight are assured, so that the driving stabilityis retained.

As the pneumatic tires 1 to be examined with the tests, tires accordingto present inventions 3 to 9 as seven models according to the presentinvention, and tires according to the conventional example 2 and aconventional example 3 as two models of conventional examples weretested by the second test method. Among the tires, the tires accordingto the conventional examples 2 and 3 had a profile form of the treadsurface 11 of the pneumatic tire 1 that was conventional and notdesigned to improve the rollover characteristics, i.e., a conventionalform. The tires according to the present inventions 3 to 9 had a profileform of the tread surface 11 that was designed to improve the rollovercharacteristics as described above, i.e., a rollover-characteristicimproved-form.

The evaluation tests were conducted on the pneumatic tires 1 accordingto the conventional example 2, the conventional example 3, and thepresent inventions 3 to 9, by the second test method. Obtained resultsare shown in FIGS. 20-1 and 20-2. Among FIGS. 20-1 and 20-2, FIG. 20-1indicates results of the evaluation tests on the tires according to theconventional example 3, and the present inventions 3 to 5, while FIG.20-2 indicates results of the evaluation tests on the tires according tothe present inventions 6 to 9.

As stated in the test results shown in FIGS. 20-1 and 20-2, the rolloverresistance can be improved by designing the profile of the tread surface11 to have the rollover-characteristic improved-form (the presentinventions 3 to 9). Furthermore, the maximum cornering force at highload can be reduced by positioning the shoulder-side circumferentialgroove 51 appropriately in the tire width direction, so that therollover resistance at high load can be improved. Moreover, anappropriate block rigidity in the vicinity of the center in the tirewidth direction can be achieved by positioning the equatorial-plane-sidecircumferential grooves 55 appropriately in the tire width direction.Accordingly, an appropriate response of the pneumatic tire 1 whencornering can be achieved, so that the driving stability can be assuredmore reliably. As a result, the rollover resistance can be improvedwhile retaining the driving stability more reliably (the presentinventions 3 to 5).

The third test method from among the seven performance evaluation testswas carried out, similarly to the second test method, by conducting atest run with a vehicle having 1300 cc of displacement fitted with thepneumatic tires 1 in the size of 185/60R15 that were mounted on therims. As an evaluation method for the performance evaluation test, theperformance evaluation tests of the rollover characteristics and thedriving stability similarly to the second test method were carried out,and an evaluation test of braking performance was further conducted.Among the tests, results of the test of the driving stability areindicated in indexes based on the evaluation result of the pneumatictire 1 according to a conventional example 6 set at 100, where thelarger index expresses the better driving stability, and when the indexis at 96 or higher, it is determined that the driving stability isretained.

In the evaluation test of the braking performance, stopping distanceswere measured by braking to a halt from 100 km/h on a dry road surfaceperformed by the antilock brake system (ABS) five times with each modelof the pneumatic tires 1 to be tested, and the average of the distanceswas taken as the stopping distance of the pneumatic tire 1 that wastested. Measurement results are indicated in indexes based on thestopping distance of the pneumatic tire 1 according to a conventionalexample 4 set at 100, where the larger index expresses the shorterstopping distance and the better braking performance.

As the pneumatic tires 1 to be examined with the tests, tires accordingto present inventions 10 to 17 as eight models according to the presentinvention, and tires according to the conventional example 4 and aconventional example 5 as two models of conventional examples weretested by the third test method. Among the tires, the tires according tothe conventional examples 4 and 5 had the profile form of the treadsurface 11 of the pneumatic tire 1 that was conventional and notdesigned to improve the rollover characteristics, i.e., the conventionalform. By contrast, the tires according to the present inventions 10 to17 had the profile form of the tread surface 11 that was designed toimprove the rollover characteristics as described above, i.e., therollover-characteristic improved-form. Moreover, on the pneumatic tires1 to be tested, the cap tread 12 was formed from one of two kinds ofrubber different in preparations of materials.

To describe more detail, the rubber that formed the cap tread 12 of thepneumatic tires 1 on which the evaluation tests were conducted by thethird test method used either rubber A or rubber B, where the rubber Awas multi purpose rubber that can be widely used for the cap tread 12,while the rubber B was high performance tire (HPT) rubber in whichmaterials were prepared to obtain a higher grip performance than therubber A. Compositions of raw materials for the rubber A and the rubberB (the proportion amount is a weight portion in a rubber weight portion100) are shown in FIGS. 21-1 and 21-2. In the figures, the compositionsof the rubber A is shown in FIG. 21-1, while the compositions of therubber B is shown in FIG. 21-2.

Each of the pneumatic tires 1 examined by the third test method had adifferent JIS-A hardness (JIS K6235) of the base rubber ply 61, and adifferent cross-sectional area ratio of the base rubber ply 61 to thetread rubber 60 (hereinafter, “the cross-sectional area ratio”).

The evaluation tests were conducted by the third test method onpneumatic tires 1 according to the conventional examples 4 and 5 and thepresent inventions 10 to 17, and obtained results are shown in FIGS.22-1 and 22-2. FIG. 22-1 indicates results of the evaluation tests onthe tires according to the conventional examples 4 and 5 and the presentinventions 10 to 12, and FIG. 22-2 indicates results of the evaluationtests on the tires according to the present inventions 13 to 17.

As stated in the test results shown in FIGS. 22-1 and 22-2, by designingthe profile of the tread surface 11 to have the rollover-characteristicimproved-form, the rollover resistance can be improved while retainingthe driving stability (the present inventions 10 to 17). Furthermore, ifthe JIS-A hardness falls within the range from 48 to 60, thecross-sectional area ratio of the base rubber ply 61 to the tread rubber60 falls within the range from 20% to 50%, and the cap tread 12 uses therubber A, the rollover resistance can be improved more reliably (thepresent inventions 10 and 11). Moreover, if the JIS-A hardness fallswithin the range from 48 to 60, the cross-sectional area ratio of thebase rubber ply 61 to the tread rubber 60 falls within the range from20% to 50%, and the cap tread 12 uses the rubber B, the drivingstability and the braking performance can be improved more reliably (thepresent inventions 12 and 13).

The fourth test method from among the seven performance evaluation testswas carried out, similarly to the second test method, by conducting atest run with a vehicle having 1300 cc of displacement fitted with thepneumatic tires 1 in the size of 185/60R15 that were mounted on therims. As an evaluation method for the performance evaluation test, theperformance evaluation tests of the rollover characteristics and thedriving stability similarly to the second test method were carried out.Among the tests, results of the test of the driving stability areindicated in indexes based on the evaluation result of the pneumatictire 1 according to the conventional example 6 set at 100, where thelarger index expresses the better driving stability, and when the indexis at 96 or higher, it is determined that the driving stability isretained.

As the pneumatic tires 1 to be examined with the tests, tires accordingto present inventions 18 to 24 as seven models according to the presentinvention, and tires according to the conventional example 6 and aconventional example 7 as two models of conventional examples weretested by the fourth test method. Among the tires, the tires accordingto the conventional examples 6 and 7 had the profile form of the treadsurface 11 of the pneumatic tire 1 that was conventional and notdesigned to improve the rollover characteristics, i.e., the conventionalform. By contrast, the tires according to the present inventions 18 to24 had the profile form of the tread surface 11 that was designed toimprove the rollover characteristics as described above, i.e., therollover-characteristic improved-form.

Each of the pneumatic tires 1 examined by the fourth test method had adifferent filler height FH of the bead filler 26, a different JIS-Ahardness (JIS K6235) Hs of the bead filler 26 at room temperature, and adifferent value G calculated in accordance with Equation (17).

The evaluation tests were conducted by the fourth test method onpneumatic tires 1 according to the conventional examples 6 and 7 and thepresent inventions 18 to 24, and obtained results are shown in FIGS.23-1 and 23-2. FIG. 23-1 indicates results of the evaluation tests onthe tires according to the conventional examples 6 and 7 and the presentinventions 18 to 20, and FIG. 23-2 indicates results of the evaluationtests on the tires according to the present inventions 21 to 24.

As stated in the test results shown in FIGS. 23-1 and 23-2, by designingthe profile of the tread surface 11 to have the rollover-characteristicimproved-form, the rollover resistance can be improved while retainingthe driving stability (the present inventions 18 to 24). Furthermore, byforming the bead core such that Equation (17) G satisfies 6≦G≦11, therollover resistance can be improved while retaining the drivingstability more reliably (the present inventions 18 to 21). Particularly,when the bead core is formed to make G satisfy 7≦G≦9, the drivingstability and the rollover resistance can be improved together (thepresent inventions 20 and 21).

The fifth test method from among the seven performance evaluation testswas carried out by conducting a test run with a sport utility vehicle(SUV) having 2400 cc of displacement, similarly to the first testmethod, fitted with the pneumatic tires 1 in the size of 225/65R17 thatwere mounted on the rims. As an evaluation method for the performanceevaluation test, the evaluation test of the rollover resistancesimilarly to the first test method, and the evaluation test of thedriving stability similarly to the second test method were conducted,and additionally an evaluation test of wear resistance was conducted.Among the tests, results of the test of the driving stability areindicated in indexes based on the evaluation result of the pneumatictire 1 according to the conventional example 8 set at 100, where thelarger index expresses the better driving stability, and when the indexis at 96 or higher, it is determined that the driving stability isretained.

As a method for the evaluation test of the wear resistance, a wearamount of the shoulder 16 on the vehicle inner side in the tire widthdirection was measured. Evaluation results are indicated in index basedon the measurement result of the tire according to a conventionalexample 8 set at 100, it is determined that the larger index expressesthe better wear resistance.

As the pneumatic tires 1 to be examined with the tests, tires accordingto present inventions 25 to 29 as five models according to the presentinvention, and tires according to the conventional example 8 as onemodel of a conventional example were tested by the fifth test method.Among the tires, according to the conventional examples 8, the profileform of the tread surface 11 of the pneumatic tire 1 was conventionaland not designed to improve the rollover characteristics, i.e., theconventional form. According to the present invention 25, the profileform of the tread surface 11 was designed to improve the rollovercharacteristics as described above, i.e., the rollover-characteristicimproved-form. According to the present inventions 26 to 29, the profileform of the tread surface 11 was asymmetrical in the tire widthdirection with respect to the equatorial plane 5, and the profile on thevehicle-outer-side in the tire width direction is in therollover-characteristic improved-form. Furthermore, according to thepresent inventions 26 and 27, the profile on the vehicle inner side inthe tire width direction is in a profile form that is designed toimprove wear resistance rather than the rollover-characteristicimproved-form. The evaluation tests were conducted on the pneumatictires 1 according to the conventional example 8, and the presentinventions 25 to 29 by the fifth test method, and obtained results areshown in FIG. 24.

As stated in the test results shown in FIG. 24, by designing the profileof the tread surface 11 at least on the vehicle-outer-side in the tirewidth direction to have the rollover-characteristic improved-form, therollover resistance can be improved while retaining the drivingstability (the present inventions 25 to 29). Furthermore, by designingthe profile of the tread surface on the vehicle-inner-side in the tirewidth direction to have a form in which K1 _(in) obtained from Equation(18) satisfies 0.4≦K1 _(in)≦0.6, K1 _(in) the wear resistance can beimproved (the present inventions 26 and 27).

The sixth test method from among the seven performance evaluation testswas carried out, similarly to the second test method, by conducting atest run with a vehicle having 1300 cc of displacement fitted with thepneumatic tires 1 in the size of 185/60R15 that were mounted on therims. As an evaluation method for the performance evaluation test, theevaluation test of the rollover resistance similarly to the second testmethod was conducted.

As the pneumatic tires 1 to be examined with the test, tires accordingto present inventions 30 to 37 as eights models according to the presentinvention, and a tire according to a conventional example 9 as one modelof a conventional example were tested by the sixth test method. Amongthe tires, according to the conventional example 9, the profile of thetread surface 11 had a conventional form. According to the presentinventions 30 to 37, the profile of the tread surface 11 had therollover-characteristic improved-form. According to the conventionalexample 9 and the present inventions 30 to 37, the belt ply 21 wasprovided with the belt cover ply 70 tire-radially outward. According tothe present inventions 31 to 37, the belt cover ply 70 was designed tohave a larger cover tensile-rigidity index Es in the shoulder region 72than a cover tensile-rigidity index Ec in the central region 71.

Specifically, the belt cover ply 70 provided on the pneumatic tire 1subjected to the evaluation tests by the sixth test method uses any oneof the reinforcing cords 75 from among five kinds that vary in materialsof the reinforcing cord 75, cord thickness, and extensibility whenextending with 50 N. Details of the reinforcing cords 75 are shown inFIG. 25.

In the pneumatic tiers 1 subjected to the evaluation tests by the sixthtest method, by using one of the reinforcing cords 75 shown in FIG. 25as the central-region reinforcing cord 76 or the shoulder-regionreinforcing cord 77 in the belt cover ply 70, the cover tensile-rigidityindex Es in the shoulder region 72 was designed to be larger than thecover tensile-rigidity index Ec in the central region 71.

The evaluation tests were conducted by the sixth test method on thepneumatic tires 1 according to the conventional example 9, and thepresent inventions 30 to 37, and obtained results are shown in FIGS.26-1 and 26-2. Among FIGS. 26-1 and 26-2, FIG. 26-1 indicates results ofthe evaluation tests on the tires according to the conventional example9, and the present inventions 30 to 33, while FIG. 26-2 indicatesresults of the revaluation tests on the tires according to the presentinventions 34 to 37.

As stated in the test results shown in FIGS. 26-1 and 26-2, by designingthe profile of the tread surface 11 to have the rollover-characteristicimproved-form, the rollover resistance can be improved (the presentinventions 30 to 37). Furthermore, by designing the belt cover ply 70 tohave the cover tensile-rigidity index Es in the shoulder region 72larger than the cover tensile-rigidity index Ec in the central region71, the rollover resistance can be improved more reliably (the presentinventions 31 to 37).

The seventh test method from among the seven performance evaluationtests was carried out by conducting a test run with a recreationalvehicle (RV) having 2400 cc of displacement fitted with the pneumatictires 1 in the size of 235/55R18 that were mounted on the rims. As anevaluation method for the performance evaluation test, the evaluationtest of the rollover resistance similarly to the first test method, andthe evaluation test of the driving stability similarly to the secondtest method were conducted, and additionally an endurance test and anevaluation test of shoulder wear were conducted. In the test of thedriving stability, results are indicated in indexes based on theevaluation result of the pneumatic tire 1 according to a conventionalexample 10 set at 100, where the larger index expresses the betterdriving stability, and when the index is at 96 or higher, it isdetermined that the driving stability is retained.

The endurance test, which was a performance test of the durability, wascarried out by conducting a low-pressure endurance test with an indoordrum test machine, and measuring the number of cracks that appearedadjacent to the shoulder 16 after running through a predetermineddistance. Measurement results are indicated in indexes based on themeasurement result of the pneumatic tire 1 according to the conventionalexample 10 in a pattern 1 set at 100, where it is determined that thelarger index expresses the better durability.

As a method of the evaluation test of the shoulder wear, the remainingamount of the lug groove 80 on the shoulder 16 was each measured tocompare measurement results. Measurement results are indicated inindexes based on a wear rate set at 100, at which the lug groove 80 onthe shoulder 16 of the pneumatic tire 1 in a size to be tested issupposed to be normally worn completely by 40,000 km. If the index islarger, it is harder to wear the shoulder, therefore, it is determinedthat the performance against the shoulder wear is good.

As the pneumatic tires 1 to be examined with the test, tires accordingto present inventions 38 to 41 as four models according to the presentinvention, and tires according to comparative examples 4 to 6 as threecomparative examples, and a tire according to the conventional example10 as one model of a conventional example were tested by the seventhtest method. The tires according to the conventional example 10, thecomparative examples 4 to 6, and the present inventions 38 to 41 wereall different in the profile of the tread surface 11. More specifically,the pneumatic tires 1 subjected to the evaluation tests in accordancewith the seventh test method, all have different profiles between theconventional example 10, the comparative example 4 to 6, and the presentinventions 38 to 41, precisely, the evaluation tests were conducted oneight profiles. The profiles are different in K1, K2, K3, and K4,obtained from Equation (11), Equation (12), Equation (13), and Equation(14), respectively, and the angle α. Details of the profiles of thepneumatic tires 1 subjected to the evaluation test by the seventh testmethod are shown in FIG. 27.

In the seventh test method, evaluation tests were conducted on each ofthe tires according to the conventional example 10, the presentinventions 38 to 41, and the comparative examples 4 to 6 with fivepatterns of the shoulder 16, namely, patterns 1 to 5 were tested. Thefive patterns have a variety of forms of the recesses 85 provided in thelug groove 80 on the shoulder 16. In the pattern 1, the recess 85 is notarranged on the shoulder 16, by contrast, in the patterns 2 to 5, therecesses 85 are arranged in the lug groove 80 on the shoulder 16. Inaddition, the recess 85 on the shoulder 16 in each of the patterns 2 to5 has a different depth.

As the pneumatic tires 1 to be examined with the seventh test method,tests of the rollover resistance, the driving stability, the durability,and the shoulder wear were conducted on each of five patterns of therecess 85 provided on the shoulder 16. Evaluation tests were conductedin accordance with the seventh test method on the pneumatic tires 1according to the conventional example 10, the present inventions 38 to41, and the comparative examples 4 to 6, and obtained results are shownin FIG. 28.

As stated in the test results shown in FIG. 28, by designing the profileof the tread surface 11 to have the rollover-characteristicimproved-form, and forming the recesses 85 on the shoulder 16, therollover characteristics can be improved while retaining the drivingstability more reliably. Furthermore, by providing the recesses 85 onthe shoulder 16, the shoulder wear can be suppressed, as a result,performance against the shoulder wear can be improved.

INDUSTRIAL APPLICABILITY

As described above, the pneumatic tire according to the presentinvention is effective, if the tread surface in the meridian crosssection is formed from a plurality of arcs. More particularly, thepneumatic tire according to the present invention is suitable, if thetread surface is formed from three arcs.

1-17. (canceled)
 18. A pneumatic tire comprising: a sidewall potionarranged on each edge of a tire width direction; and a tread portionprovided on an outer side of the sidewall potion in a tire radialdirection, the tread portion including a cap tread, wherein a treadsurface that is a surface of the cap tread in a meridian cross sectionof the pneumatic tire is formed with a plurality of arcs with differentcurvature radiuses, under a condition when the pneumatic tire is mountedon a proper rim, and filled with an internal pressure of 5% of a normalinternal pressure, the tread surface is formed from a center arccentered in the tire width direction, a shoulder-side arc positioned ona vehicle-outer-side at least from the center arc in the tire widthdirection, and a shoulder arc that forms a shoulder arranged at least avehicle-outer-side end in the tire width direction of the tread surface,K1 satisfies 0.6≦K1≦0.8, K2 satisfies 0.9≦K1≦2.0, and K3 satisfies0.40≦K3≦0.48, where K1 is defined by K1=L1/(TDW×0.5), K2 is defined byK2=TR1/OD, K3 is defined by K3=(β×TDW)/(100×SW), TR1 is a curvatureradius of the center arc, L1 is an outline area, which is a width froman equatorial plane to an end of the center arc in the tire widthdirection, TDW is a tread development width, which is a width of thetread surface in the tire width direction, SW is a total width, which isa width in the tire width direction between outermost positions in thetire width direction of the sidewall potions opposed as arranged at bothedges of the tire width direction, OD is a tire outside diameter, whichis a diameter of the pneumatic tire at a position at which a diameter ofthe tread surface in a tire-radial direction is largest, and β is anaspect ratio.
 19. The pneumatic tire according to claim 18, wherein anangle α formed by a tangent in contact with the center arc and a tangentin contact with the shoulder arc satisfies 35°≦α≦60°, the tangent incontact with the center-arc passing through an end in the tire widthdirection of the center-arc, and the tangent in contact with theshoulder-arc passing through an outer end in the tire width direction ofthe shoulder arc.
 20. The pneumatic tire according to claim 18, whereinK4 satisfies 0.025≦K4≦0.035, where K4 is defined by K4=SHR/TR1, and SHRis a curvature radius of the shoulder arc.
 21. The pneumatic tireaccording to claim 18, wherein at least a part of the cap tread uses acompound of which a 300%-tensile modulus is 5 megapascal to 10megapascal.
 22. The pneumatic tire according to claim 18, wherein atleast a part of the cap tread uses anisotropic rubber in which a modulusin the tire width direction is smaller than a modulus in tirecircumferential direction.
 23. The pneumatic tire according to claim 18,wherein a plurality of circumferential grooves that are formed in a tirecircumferential direction are further provided on the tread surface, anda shoulder-side circumferential groove from among the circumferentialgrooves that is a circumferential groove arranged most closely to theshoulder between the equatorial plane and the shoulder is provided at aposition at which T1 satisfies 0.55≦T1≦0.65, where T1 is defined byT1=H1/(TDW×0.5), and H1 is a distance from a groove-width center of theshoulder-side circumferential groove to the equatorial plane in the tirewidth direction.
 24. The pneumatic tire according to claim 23, whereinan equatorial-plane-side circumferential groove from among thecircumferential grooves that is a circumferential groove arranged mostclosely to the equatorial plane between the equatorial plane and theshoulder is provided at a position at which T2 satisfies 0.15≦T2≦0.20,where T2 is defined by T2=H2/(TDW×0.5), and H2 is a distance from agroove-width center of the equatorial-plane-side circumferential grooveto the equatorial plane in the tire width direction.
 25. The pneumatictire according to claim 18, wherein the tread portion is formed fromtread rubber that includes at least the cap tread, and a base rubber plythat is arranged tire-radially inward from the cap tread, the baserubber ply has a JIS-A hardness between 48 and 60 at room temperature,and a cross sectional area of the base rubber ply in the meridian crosssection is within a range between 20% to 50% of a cross sectional areaof the tread rubber.
 26. The pneumatic tire according to claim 18,wherein a bead in which a bead core is arranged is providedtire-radially inward on the sidewall potion, and a bead filler isprovided tire-radially outward from the bead core, and G satisfies6≦G≦11, where G is defined by G=(Hs×FH)/(OD×β), Hs is a JIS-A hardnessof the bead filler at room temperature, and FH is a filler height, whichis a distance between an outward edge and a most distant point in thebead filler, the outward edge being a position tire-radially mostoutward of the bead filler in the meridian cross section.
 27. Thepneumatic tire according to claim 18, wherein a relation between K1_(in) and K1 satisfies K1 _(in)≦K1×0.9, where the outline area on thevehicle-outer-side in the tire width direction differs from that on thevehicle inner side in the tire width direction, the outline area LI isthe outline area on the vehicle-outer-side in the tire width direction,and the K1 is a relation between the outline area L1 on thevehicle-outer-side in the tire width direction, and the treaddevelopment width TDW, L1 _(in) is the outline area on the vehicle innerside in the tire width direction, and K1 _(in) is defined by K1 _(in)=L1_(in)/(TDW×0.5), which is a relation between the outline area L1 _(in)and the tread development width TDW.
 28. The pneumatic tire according toclaim 27, wherein the K1 _(in) in satisfies 0.4≦K1 _(in)≦0.6.
 29. Thepneumatic tire according to claim 18, wherein a belt ply is providedtire-radially inward from the tread portion, and a cover belt ply isprovided tire-radially outward from the bracing ply, the cover plyincludes a central region that contains a reinforcing cord and iscentered in the tire width direction, and shoulder regions that arepositioned on both sides of the central region in the tire widthdirection, and a ratio of a cover tensile-rigidity index Ec in thecenter region to a cover tensile-rigidity index Es in the shoulderregion satisfies 1.0<Es/Ec, where the cover tensile-rigidity index Ec inthe center region is defined by Ec=Dc/Sc, where Dc is number ofreinforcing cords per 50 millimeters in a direction of arrangement ofthe reinforcing cord arranged in the center region, and Sc is anextension rate (%) of one of the reinforcing cords arranged in thecenter region when a load of 50 Newton is applied, the covertensile-rigidity index Es in the shoulder region is defined by Es=Ds/Ss,where Ds is number of reinforcing cords per 50 millimeters in adirection of arrangement of the reinforcing cord arranged in theshoulder region, and Ss is an extension rate (%) of one of thereinforcing cords arranged in the shoulder region when a load of 50Newton is applied.
 30. The pneumatic tire according to claim 18, whereina lug groove is formed on the shoulder, and a recess is formed at agroove bottom of the lug groove outward from a contact end of the treadportion in the tire width direction.
 31. The pneumatic tire according toclaim 30, wherein a depth H and an average D satisfy 0.20≦H/D≦0.50,where H is a depth of the recess at a deepest point, and D is an averageof groove depths D1 and D2 of the lug groove at both ends of the recessin the tire width direction.
 32. The pneumatic tire according to claim30, wherein, in the recess, an opening area decreases from an opening ofthe recess toward a deepest point of the recess.
 33. The pneumatic tireaccording to claim 30, wherein the recess is arranged between a contactend and a limit contact end, when the limit contact end is set at apoint distant 1.3 times of a distance from a center of contact width ofthe tread portion to the contact end.
 34. The pneumatic tire accordingto claim 30, wherein, in the recess, a cross sectional area graduallyincreases as toward outward in the tire width direction.